Title of Invention: EXTERNAL PULSE GENERATOR DEVICE AND AFFIXATION DEVICE FOR TRIAL NERVE STIMULATION AND METHODS OF USE Abstract: Systems and methods for providing a trial neurostimulation to a patient for assessing suitability of a permanently implanted neurostimulation are provided herein. In one aspect, a trial neurostimulation system includes an EPG affixation device that secures the EPG to the patient when connected to a lead extending through a percutaneous incision to a target tissue location, while allowing for ready removal of the EPG for charging or bathing. In another aspect, the system includes an EPG provided with a multi-purpose connector receptacle through which the the EPG can deliver neurostimulation therapy to an implanted lead or the EPG can be charged. In yet another aspect, the EPG can include a multi-purpose connector receptacle that is alternatingly connectable with a plurality of differing connector to facilitate differing types of therapies with one or more neurostimulation devices, ground patches or various other devices, such as charging or testing devices. Detailed Description: CROSS-REFERENCES TO RELATED APPLICATIONS The present application is a continuation of U.S. Non-Provisional application Ser. No. 15/431,475, filed on Feb. 13, 2017, which claims the benefit of priority to U.S. Provisional Application 62/294,639 filed Feb. 12, 2016, the entire contents of which are incorporated herein by reference. The present application is related to U.S. Non-Provisional application Ser. No. 14/827,081, entitled External Pulse Generator Device and Associated Methods for Trial Nerve Stimulation” filed on Aug. 14, 2015, the entire contents of which are incorporated herein by reference in its entirety for all purposes. BACKGROUND OF THE INVENTION Treatments with implanted neurostimulation systems have become increasingly more common in recent years. While such systems have shown promise in treating a number of chronic conditions, effectiveness of treatment may vary considerably between patients and viability of treatment can be difficult to determine before implantation. Although conventional methods of implantation often utilize preliminary testing with a temporary, partly implanted neurostimulation systems to assess viability of treatment, such systems may not provide an accurate representation of treatment with a fully implanted device. In addition, such systems are often bulky, uncomfortable and limit patient mobility, such that many patients elect not to receive a temporary system or a fully implanted system. In addition, many such temporary partly implanted systems may not operate in the same manner as their fully implanted counterparts due to differences between pulse generators or changes in position of the neurostimulation leads during conversion. Therefore, it is desirable to provide methods and devices for providing trial treatment systems that provide a more accurate representation of treatment, improve patient comfort and provide consistent treatment outcomes as compared to fully implanted neurostimulation systems. BRIEF SUMMARY OF THE INVENTION The present invention relates to neurostimulation treatment systems, and in particular a neurostimulation treatment system having an EPG with a multi-purpose connector receptacle and affixation devices on which the EPG is releasably mounted and that are secured to the patient during a trial neurostimulation treatment. Typically, such a trial neurostimulation treatment includes a partly implanted neurostimulation lead extending to an external pulse generator for conducting a trial neurostimulation treatment for assessing viability of a fully implanted system. In one aspect, the system includes a partly implanted neurostimulation lead that extends from one or more implanted neurostimulation electrodes to an external pulse generator (EPG) supported in an affixation device secured to the patient. In some aspects, the trial period may be as little as 4-7 days, while in other aspects the trial period may extend two weeks or more, typically about two weeks. In one aspect, an external pulse generator is provided that includes an outer housing having at least one port and a connector receptacle accessed via the port. The receptacle can be adapted for receivably coupling with a proximal portion of an implantable neurostimulation lead to electrically couple the external pulse generator with one or more neurostimulation electrodes of the neurostimulation lead implanted at a target tissue. The external pulse generator further includes a pulse generator electrically coupled with the connector receptacle and adapted for generating neurostimulation pulses to one or more neurostimulation electrodes of the lead. The connector receptacle can be configured to support various types of neurostimulation lead, including a Peripheral Nerve Evaluation (PNE) lead (bilateral or unilateral) as well as a tined lead. The external pulse generator can further include a rechargeable battery electrically coupled to the pulse generator and connector receptacle that is configured for recharging by electrical power delivered via the connector receptacle. In some embodiments, the external pulse generator can include electrical circuitry coupling each of the pulse generator, the rechargeable battery and the connector receptacle. The circuitry is configured, by programmable instructions recorded on a memory thereof, to power the pulse generator with the charged battery and charge the battery with electrical power delivered via the connector receptacle. The circuitry can further be configured to switch between differing operating modes of the external pulse generator, which can include a therapy mode and a charging mode. In some embodiments, the circuitry is configured to switch to the charging mode when the connector receptacle is coupled to power connector of a charging cord coupled to an external power source. The circuitry can also be configured to switch to the therapy mode when the connector receptacle is coupled to the proximal connector of the neurostimulation lead. The circuitry can further be adapted for suspending pulse generation in response to disconnecting the neurostimulation lead. Suspending pulse generation can be performed in response to a detection of loss of electrical connectivity within the connector receptacle while in the therapy mode. This capability serves as a safety feature and can be included in any EPG, including multi-port EPGs, regardless of whether a rechargeable or a permanent battery is used. In some embodiments, an external pulse generators can include circuitry configured for switching to the charging mode by electrically connecting the battery to the receptacle while operatively disconnecting the battery from the pulse generator, and switching to the therapy mode by operatively connecting the pulse generator to the battery and electrically disconnecting the battery from the receptacle. In some embodiments, the external pulse generator includes one or more stimulation programs operable within the therapy mode for use in one or more trial stimulation periods. In some embodiments, the external pulse generator is reusable such that it can be reused in multiple trials and/or with multiple patients. These aspects allow for improved versatility and makes a trial nerve stimulation more accessible to a wide range of patient populations. In another aspect, such a trial system can include an external pulse generator with a multi-purpose connector receptacle. Such an external pulse generator can be configured with a single connector receptacle. The connector receptacle can be adapted for alternatingly connecting with a plurality of differing connectors, which can include a proximal lead connector of a neurostimulation lead and a power connector of a charging cord. In some embodiments, the circuitry is adapted for charging the battery when the charging cord is electrically coupled with a standard 120 volt outlet. The differing types of connectors can further include multiple differing connectors associated with differing cable sets, each suited for a particular purpose. Such differing connectors can include a first connector on a proximal portion of the neurostimulation lead; a second connector coupled in parallel to each of a ground and one or more proximal connectors of one or more implantable neurostimulation leads each having one or more neurostimulation electrodes, typically one or two proximal connectors of one or two neurostimulation leads; a third connector coupled in parallel to two or more proximal connectors of neurostimulation leads; and a fourth connector coupled with a charging cord and adapted for use in charging a rechargeable battery of the external pulse generator. In another aspect, methods of performing a neurostimulation treatment during a trial period are provided herein. Such a method can include, first, electrically coupling a neurostimulation lead to an external pulse generator, the lead including one or more neurostimulation electrodes implanted at or near a targeted tissue within the patient. The neurostimulation treatment can then be delivered to the one or more neurostimulation electrodes with the external pulse generator. To facilitate charging, a rechargeable battery of the external pulse generator can be electrically coupled with an external power source via the first receptacle port of the external pulse generator, after which the battery is charged with the external power source. In some embodiments, delivering the neurostimulation lead can be performed in a neurostimulation operating mode of the external pulse generator, while charging of the external pulse generator can be performed in a charging operating mode. Such methods can further include: switching to the neurostimulation mode upon connection of the neurostimulation lead; and switching to the charging mode upon connection of a charging cord connected to an external power source and/or grounding. In yet another aspect, an external pulse generator affixation device for securing an external pulse generator on a patient is provided herein. Such affixation devices can include a substrate having a patient coupling feature disposed along a first side and a mounting portion disposed along a second side opposite the first side. The mounting portion can include a plurality of tabs that engage the external pulse generator along an outer perimeter thereof so as to releasably couple the external pulse generator with the substrate. The plurality of tabs can be dimensioned and arranged so that a majority of the outer perimeter remains exposed to allow a patient to readily detach the external pulse generator from the adhesive patch while coupled to the patient. In some embodiments, the tabs are dimensioned and arranged so that about ⅔ or more of the outer perimeter remains exposed, or so that about ⅘ or more of the outer perimeter remains exposed, or so that about 9/10 or more of the perimeter remains exposed. In embodiments where the EPG is of a substantially rectangular shape, the multiple tabs can be arranged such that at least two diagonally opposing corners, or even all four corners, of the substantially rectangular EPG are exposed so that the EPG can be removed by grasping and engaging the corners of the EPG while secured within the affixation device. In some embodiments, the mounting portion is non-electrically conductive. Typically, the affixation device is without any electrodes or electrically conductive path by which stimulation can be delivered to a skin of the patient. In some embodiments, the affixation device includes a mounting portion with multiple tabs that include at least two resiliently deflectable tabs, each having a retention feature that engages an outer housing of an external pulse generator so as to releasably secure the external pulse generator to the substrate. The retention features of each of the at least two deflectable tabs can be adapted to be received within corresponding retention features on opposite sides of the external pulse generator. In some embodiments, the retention features of each tab comprises a contoured or stepped portion of each tab and the retention feature of the external pulse generator includes a retention recess having a corresponding contour or stepped portion for receiving the retention features of the at least two tabs. When the external pulse generator is substantially rectangular in shape, the at least two resiliently deflectable tabs can be adapted to engage opposing sides of the external pulse generator along a length dimension of the external pulse generator. In some embodiments, the mounting portion can include at least two additional tabs that engage opposing sides of the external pulse generator along a width dimension. In some embodiments, the at least two deflectable tabs and/or the at least two additional tabs engage the external pulse generator along a mid-portion thereof so that the external pulse generator can be removed by grasping the exposed sides and/or corners and twisting the external pulse generator along one or more axes. In some embodiments, the affixation device includes an EPG mounting portion with multiple tabs that include a first pair of deflectable tabs adapted to engage opposite sides of the external pulse generator along a first axis to constrain movement along the first axis and a second pair of deflectable tabs adapted to engage opposite sides of the external pulse generator along a second axis substantially orthogonal to the first axis to constrain movement along the second axis. The second pair of deflectable tabs can each include a retention feature that engages a corresponding retention feature of the external pulse generator to constrain movement along a third axis orthogonal to each of the first and second axis. In this aspect, the plurality of tabs, in combination, constrain movement of the external pulse generator relative the substrate in all three dimensions. The substrate can be substantially rigid or semi-rigid between the multiple tabs so as to maintain the relative position and orientations of the tabs. In some embodiments, the patient coupling feature of the affixation device is a flexible adhesive patch having a pressure-sensitive adhesive with sufficient strength to support an external pulse generator mounted on the adhesive patch adhered to a skin of the patient. In other embodiments, the patient coupling feature is a clip having an elongate member extending along and separable from the substrate. The clip can be biased towards the substrate so that the device is securable by insertion of a portion of a garment or belt between the elongate member and the substrate. The elongate clip member can be pivotally coupled to the substrate and biased toward the substrate is loaded with a spring. In another aspect, the EPG includes a pulse generator electrically configured for generating neurostimulation pulses along multiple stimulation channels, a battery electrically coupled to the pulse generator, an outer housing enclosing the pulse generator and battery, and a multi-pin connector electrically coupled with the pulse generator through an external cable extending from the housing. The multi-pin connector includes multiple pins that correspond to the multiple channels. In some embodiments, the external cable is permanently attached to the housing such that any electrical connections between the multi-pin connector and the pulse generator are permanently sealed. Typically, the external cable is between 1 inch and 12 inches in length. In some embodiments, the battery is non-removable by the patient. In some embodiments, the battery is non-rechargeable. In some embodiments, the EPG includes an actuatable user interface feature, such as a button or switch, that is disposed on the housing and configured for initiating wireless communication with an external programmer when actuated. In some embodiments, the actuatable user interface is configured such that actuation while the pulse generator is off or in a hibernation state causes the EPG to be receptive to or initiate wireless communication with the external programmer for a pre-determined period of time, and operation or communication by the EPG remains unchanged when actuation occurs while the pulse generator is operating or communicating. The pre-determined period of time can be any suitable period of time, for example 30 seconds or more, typically about 60 to 90 seconds. In some embodiments, the EPG is configured such that if no communication is established with the external programmer during the pre-determined period of time, the EPG returns to a hibernation or off state. Typically, the EPG is wirelessly coupleable with a patient remote and configured to turn off stimulation during operation in response to a command received from the patient remote. In some embodiments, the EPG further includes a status indicator interface disposed on the housing and configured to indicate status of: a communication between the EPG and an external programmer, an operating state, a battery level, an error state, or any combination thereof. In some embodiments, the EPG housing has opposing major faces, a contoured top surface and a flattened underside surface for placement against the patient when the EPG is worn during a trial period. In some embodiments, the status indicator interface and the actuatable user interface are disposed on the underside surface of the housing of the EPG. In another aspect, the trial system includes an EPG having a multi-pin connector and multiple connectors selectively coupleable within the multi-pin connector. The multiple connectors including at least two of: a first connector on a proximal portion of the neurostimulation lead, a second connector coupled in parallel to each of a ground and one or more proximal connectors of one or more implantable neurostimulation leads, each having one or more neurostimulation electrodes on a distal portion thereof, and a third connector coupled in parallel to two or more proximal connectors of two or more neurostimulation leads. In some embodiments, the trial system includes one or more connector cables coupleable with the multi-pin connector and one or more neurostimulation leads. In some embodiments, the one or more connectors can include a lead extension cable extending between a corresponding multi-pin connector and at least one implantable lead connector having a receptacle configured for receiving a proximal lead connector of a fully implantable neurostimulation lead. In some embodiments, the one or more connectors include a multi-lead cable extending between a corresponding multi-pin connector and multiple lead connectors, each having a lead receptacle for coupling with a neurostimulation lead, and at least one ground connector for coupling with a ground patch. Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating various embodiments, are intended for purposes of illustration only and are not intended to necessarily limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration of a trial neurostimulation system having a partly implanted lead extending to an EPG patch adhered to the skin of the patient, in accordance with some embodiments of the invention. FIGS. 2A and 2B are example overviews of the neurostimulation system of FIG. 1. FIG. 3A is an alternative configuration of a trial neurostimulation system, in accordance with some embodiments. FIG. 3B is yet another alternative configuration of a trial neurostimulation system, in accordance with some embodiments. FIG. 3C is a detail of the neurostimulation system in FIG. 3. FIGS. 4A-4C are overhead and side views of an example EPG affixation patch, in accordance with some embodiments. FIG. 5 illustrates an EPG and an associated schematic in accordance with some embodiments. FIG. 6 shows a schematic of an EPG in accordance with some embodiments. FIGS. 7A-7B illustrate an alternative EPG in accordance with some embodiments. FIG. 7C shows an exploded view of the EPG in FIGS. 7A-7B. FIGS. 8A-8B illustrate an EPG and affixation device for use in a trial neurostimulation system in accordance with some embodiments. FIGS. 9A-9B illustrate an EPG and affixation device for use in a trial neurostimulation system in accordance with some embodiments. FIG. 10 illustrates an example EPG supported in a pouch of a belt for use in a trial neurostimulation system in accordance with some embodiments. FIG. 11 illustrates an example EPG covered by an adhesive patch or tape for use in a trial neurostimulation system in accordance with some embodiments. FIGS. 12A-12F illustrate an example EPG and alternate connector cables adapted for varying uses in accordance with some embodiments. FIG. 13 illustrates an alternative percutaneous extension cable in accordance with some embodiments. FIG. 14 illustrates an alternative basic trial cable in accordance with some embodiments. FIG. 15 schematically illustrates a use of a trial neurostimulation system utilizing an EPG affixation device in accordance with some embodiments. FIGS. 16-17 illustrate methods of performing a trial neurostimulation therapy in accordance with some embodiments. DETAILED DESCRIPTION OF THE INVENTION Neurostimulation has been used for many years to treat a variety of conditions, from chronic pain, to erectile dysfunction and various urinary dysfunctions. While neurostimulation has proven effective in many applications, effective therapy often relies on consistently delivering therapeutic activation by one or more neurostimulation electrodes to particular nerves or targeted regions with a pulse generator. In recent years, fully implantable neurostimulation have become increasingly more commonplace. Although such implantable systems provide patients with greater freedom and mobility, the neurostimulation electrodes of such systems are more difficult to adjust once they are implanted. The neurostimulation electrodes are typically provided on a distal end of an implantable lead that is advanced through a tunnel formed in a patient tissue. FIG. 1 schematically illustrates a use of a trial neurostimulation system utilizing an EPG affixation device, in accordance with aspect of the invention. Such a trial neurostimulation system can be used to assess viability of a fully implantable neurostimulation system. Implantable neurostimulation systems can be used in treating patients with, for example, chronic, severe, refractory neuropathic pain originating from peripheral nerves or various urinary and bowel dysfunctions. Implantable neurostimulation systems can be used to either stimulate a target peripheral nerve or the posterior epidural space of the spine. An implantable neurostimulation system includes an implanted pulse generator, typically implanted in a lower back region. In some embodiments, the pulse generator can generate one or more non-ablative electrical pulses that are delivered to a nerve to control pain or cause some other desired effect. In some applications, the pulses having a pulse amplitude of between 0-1,000 mA, 0-100 mA, 0-50 mA, 0-25 mA, and/or any other or intermediate range of amplitudes may be used. One or more of the pulse generators can include a processor and/or memory adapted to provide instructions to and receive information from the other components of the implantable neurostimulation system. The processor can include a microprocessor, such as a microprocessor from Intel® or Advanced Micro Devices, Inc.®, or the like. An implantable pulse generator may implement an energy storage feature, such as one or more capacitors or a battery, and typically includes a wireless charging unit. The electrical pulses generated by the pulse generator are delivered to one or more nerves and/or to a target location via one or more leads that include one or more neurostimulation electrodes at or near the distal end. The leads can have a variety of shapes, can be a variety of sizes, and can be made from a variety of materials, which size, shape, and materials can be dictated by the application or other factors. In some applications, the leads may be implanted to extend along the spine or through one of the foramen of the sacrum, such as shown in FIG. 1, such as in sacral nerve stimulation. In other applications, the leads may be implanted in a peripheral portion of the patient's body, such as in the arms or legs, and can be configured to deliver one or more electrical pulses to the peripheral nerve such as may be used to relieve chronic pain. One or more properties of the electrical pulses can be controlled via a controller of the implanted pulse generator. In some embodiments, these properties can include, for example, the frequency, strength, pattern, duration, or other aspects of the timing and magnitude of the electrical pulses. These properties can include, for example, a voltage, a current, or the like. This control of the electrical pulses can include the creation of one or more electrical pulse programs, plans, or patterns, and in some embodiments, this can include the selection of one or more pre-existing electrical pulse programs, plans, or patterns. In the embodiment depicted in FIG. 1, the implantable neurostimulation system 100 includes a controller in the implantable pulse generator having one or more pulse programs, plans, or patterns and/or to select one or more of the created pulse programs, plans, or patterns. Sacral neuromodulation (SNM), also known as sacral nerve stimulation (SNS), is defined as the delivery of mild electrical pulses to the sacral nerve to modulate the neural pathways controlling bladder and rectal function. This policy addresses use of SNM in the treatment of urinary or fecal incontinence, urinary or fecal nonobstructive retention, or chronic pelvic pain in patients with intact neural innervation of the bladder and/or rectum. Treatment using SNM, also known as SNS, is one of several alternative modalities for patients with fecal incontinence, or overactive bladder (urge incontinence, significant symptoms of urgency-frequency) or nonobstructive urinary retention who have failed behavioral (e.g., prompted voiding) and/or pharmacologic therapies. Urge incontinence is defined as leakage of urine when there is a strong urge to void. Urgency-frequency is an uncontrollable urge to urinate, resulting in very frequent small volumes. Urinary retention is the inability to completely empty the bladder of urine. Fecal incontinence is the inability to control bowel movements resulting in unexpected leakage of fecal matter. The SNM device consists of an implantable pulse generator that delivers controlled electrical impulses. This pulse generator is attached to wire leads that connect to the sacral nerves, most commonly the S3 nerve root. Two external components of the system help control the electrical stimulation. A patient remote control may be kept by the patient and can be used to control any of the variety of operational aspects of the EPG and its stimulation parameters. In one such embodiment, the patient remote control may be used to turn the device on or return the EPG to a hibernation state or to adjust stimulation intensity. A console programmer is kept by the physician and used to adjust the settings of the pulse generator. In a conventional approach, prior to implantation of the permanent device, patients undergo an initial testing phase to estimate potential response to treatment. The first type of testing developed was percutaneous nerve evaluation (PNE). This procedure is done under local anesthesia, using a test needle to identify the appropriate sacral nerve(s). Once identified, a temporary wire lead is inserted through the test needle and left in place for 4 to 7 days. This lead is connected to an external stimulator, which can be carried by patients in their pocket, secured against the skin under surgical dressings, or worn in a belt. The results of this test phase are used to determine whether patients are appropriate candidates for the permanent implanted device. For example, for overactive bladder, if patients show a 50 percent or greater reduction in symptom frequency, they are deemed eligible for the permanent device. The second type of testing is a 2-stage surgical procedure. In Stage 1, a quadripolar-tined lead is implanted (stage 1). The testing phase can last as long as several weeks, and if patients show a specified reduction in symptom frequency, they can proceed to Stage 2 of the surgery, which is permanent implantation of the neuromodulation device. The 2-stage surgical procedure has been used in various ways. These include its use instead of PNE, for patients who failed PNE, for patients with an inconclusive PNE, or for patients who had a successful PNE to further refine patient selection. In one aspect, the duration of battery life of the EPG is at least four weeks for a tined lead at nominal impedance (e.g. about 1200 Ohms), an amplitude of about 4.2 mA, and a pulse width of about 210 us, or the duration of battery life can be at least seven days for a PNE lead. In some embodiments, the battery is rechargeable and can be recharged by coupling the battery with a standard 120 V wall outlet, and may optionally utilize the same power cables or adapter as used by other system components (e.g. clinician programmer). Typically, the EPG is current controlled. The EPG can be configured with a pulse width between 60-450 μs, a maximum stimulation rate between 2 and 130 Hz, a maximum amplitude between 0 and 12.5 mA, a stimulation waveform that is biphasic charge-balanced assymetric, minimum amplitude steps of about 0.05 mA, continuous or cycling operating modes, a set number of neurostimulation programs (e.g. two programs), ramping capability, and optional alert built into the EPG. The permanent device is implanted under local or general anesthesia. An incision is made over the lower back and the electrical leads are placed in contact with the sacral nerve root(s). The wire leads are extended underneath the skin to a pocket incision where the pulse generator is inserted and connected to the wire leads. Following implantation, the physician programs the pulse generator to the optimal settings for that patient. One example of a common process for treating bladder dysfunction is to employ a trial period of sacral neuromodulation with either a percutaneous lead or a fully implanted lead in patients that meet all of the following criteria: (1) a diagnosis of at least one of the following: urge incontinence; urgency-frequency syndrome; non-obstructive urinary retention; (2) there is documented failure or intolerance to at least two conventional therapies (e.g., behavioral training such as bladder training, prompted voiding, or pelvic muscle exercise training, pharmacologic treatment for at least a sufficient duration to fully assess its efficacy, and/or surgical corrective therapy); (3) the patient is an appropriate surgical candidate; and (4) incontinence is not related to a neurologic condition. Permanent implantation of a sacral neuromodulation device may be considered medically necessary in patients who meet all of the following criteria: (1) all of the criteria (1) through (4) in the previous paragraph are met; and (2) trial stimulation period demonstrates at least 50% improvement in symptoms over a period of at least one week. Other urinary/voiding applications of sacral nerve neuromodulation are considered investigational, including but not limited to treatment of stress incontinence or urge incontinence due to a neurologic condition, e.g., detrusor hyperreflexia, multiple sclerosis, spinal cord injury, or other types of chronic voiding dysfunction. (See policy description of sacral nerve neuromodulation/stimulation coverage provided by Blue Cross Blue Shield available online at: http://www.bcbsms.com/com/bcbsms/apps/PolicySearch/views/ViewPolicy. php?&noprint=yes&path=%2Fpolicy%2Femed%2FSacral_Nerve_Stimulation.html) In another conventional approach, a similar method is used in peripheral neurostimulation (PNS) treatment systems. Generally, candidates for peripheral neurostimulation are assessed to determine their suitability for undergoing the PNS procedure. Prior to the surgery, the patient will undergo pre-surgical testing that includes routine blood tests as well as neuropsychological evaluation. The PNS procedure itself is typically performed in two separate stages. Each stage takes about one hour, and the patient can go home the same day. In this aspect, Stage 1 involves implanting of trial electrodes, via small needles, which are connected to an external pulse generator (EPG), typically worn on a belt of the patient. A number of stimulation programs are administered over the next few days. If this trial demonstrates a significant improvement in the patient's headache or facial pain, permanent implantation can take place. In Stage 2, a new set of electrodes, the width of angel-hair pasta, are implanted under the skin. These are connected to a smaller implantable pulse generator implanted under the skin in the chest, abdomen, or back. Among the drawbacks associated with these conventional approaches, is the discomfort associated with wearing an EPG. The effectiveness of a trial period such as in PNE and Stage 1 trial periods are not always indicative of effective treatment with a permanent implanted system. In one aspect, since effectiveness of treatment in a trial period may rely, in part, on a patient's subjective experience, it is desirable if the discomfort and inconvenience of wearing an EPG by the patient can be minimized so that the patient can resume ordinary daily activities without constant awareness of the presence of the EPG and treatment system. This aspect can be of particular importance in treatment of overactive bladder and erectile dysfunction, where a patient's awareness of the device could interfere with the patient's experience of symptoms associated with these conditions. In one aspect, the invention allows for improved assessment of efficacy during trial periods by providing a trial system having improved patient comfort so that patients can more easily recognize the benefits and effectiveness of treatment. In another aspect, the portions of the EPG delivering the therapy are substantially the same as the IPG in the permanent system such that the effects in permanent treatment should be more consistent with those seen in the trial system. In certain embodiments, the invention provides an EPG patch worn on a skin of the patient so as to improve patient comfort. Optionally, the EPG used in Stage 1 may be smaller than the IPG used in the corresponding Stage 2 so that the EPG can easily be supported by and sealed against contamination by an adherent patch that covers the EPG. In one aspect, the EPG is a modified version of the implantable IPG used in Stage 2. The IPG may be modified by removal of one or more components, such as removal of a remote charging coil with a smaller battery and associated components. In addition, the EPG may use a thinner, lighter housing than the IPG, since the EPG is not required to last for many years, such as the IPG would be. The EPG therefore, may be configured to be disposable. These aspects allow the EPG to be supported within a patch adhered to the skin of the patient at a convenient and comfortable location. FIG. 1 illustrates an example trial neurostimulation system 100 having an EPG patch 10. As shown, the neurostimulation system is adapted to stimulate a sacral nerve root. The neurostimulation system 100 includes an implantable pulse generator (IPG) implanted in a lower back region, from which a neurostimulation lead 20 extends through a foramen of the sacrum to electrodes (not shown) disposed near the sacral root. The neurostimulation lead 20 further includes an anchor 10 disposed on a dorsal side of the sacrum. It is appreciated, however, that the anchor may be disposed on a ventral side of the sacrum as well, or within the foramen itself. In one aspect, the EPG 40 is disposable and discarded after the trial is complete. Typically, the trial may last anywhere from 4 days to 8 weeks. Typically, an initial assessment may be obtained after 4-7 days and, if needed, effectiveness of treatment may be examined after a few weeks, typically about 2 weeks. In one aspect, the EPG 40 of the EPG patch 10 is of a substantially similar design as the IPG that would be implanted if the trial proves successful, however, one or more components may be removed to allow the EPG to be smaller in size, lower in mass, and/or differing materials are used since the device may be intended for one time use. FIG. 2A shows an embodiment of neurostimulation system 100, similar to that in FIG. 1, in more detail. As can be seen, the neurostimulation lead 20′ includes a neurostimulation electrode 30 at a distal end configured for PNE use. The EPG 40 is supported within an adherent patch 11 when attached to a skin of the patient. FIG. 2B illustrates an alternate embodiment of neurostimulation system 100, similar to that in FIG. 1, in more detail. Neurostimulation lead 20 is attached to EPG 40 via extension cable 22 and connector 21. As can be seen, the neurostimulation lead 20 includes a plurality of neurostimulation electrodes 30 at a distal end of the lead and an anchor 50 having a plurality of tines disposed just proximal of the electrodes 30. Typically, the anchor is disposed near and proximal of the plurality of electrodes so as to provide anchoring of the lead relatively close to the electrodes. The EPG 40 is supported within an adherent patch 11 when attached to a skin of the patient. In one aspect, additional adherent patches 16 may be used to cover and seal the percutaneous incision in the skin of the patient through which the percutaneous portion of the neurostimulation lead is inserted. The lead may be secured at the percutaneous incision with surgical tape 17 and further secured and sealed with an adherent patch covering the lead and percutaneous incision. In this manner, the percutaneous incision can be sealed and protected from contamination or infection and its position maintained by the additional adherent patches 16. This configuration reduces the likelihood of infection and prevents movement of the lead, both internal and external, such that the patient's awareness of the patch and lead is minimized, thereby allowing the patient to resume relatively normal daily activities. In another aspect, since the EPG patch may be worn in a different location, such as on the abdomen, than the IPG would be implanted, to allow the IPG to use the same fully implanted neurostimulation lead 20, the system may use a lead extension 22 coupled with the lead 20 by an implanted connector 21. The lead extension 22 may optionally be hardwired into the EPG so as to eliminate potential disconnection and allow the connection to be sealed or encapsulated within the adherent patch so as to be water resistant or water proof. This allows the patient to perform routine daily activities, such as showering without removing the device. The length of lead 20 may be a suitable length for the permanently implanted system, while the length of extension 22 allows the lead to EPG patch to be positioned in a location that provide improved comfort and minimized interference with daily activities. FIG. 3A illustrates an alternate configuration in which the lead is sufficiently long to allow the EPG patch 10 to be placed to allow the patient more mobility and freedom to resume daily activities that does not interfere with sitting or sleeping. Excess lead can be secured by an additional adherent patch 16, as shown by the center patch in FIG. 3A. In one aspect, the lead is hardwired to the EPG, while in another the lead is removable connected to the EPG through a port or aperture in the top surface of the flexible patch 11. In one aspect, the EPG patch and extension cable are disposable such that the implanted lead can be disconnected and used in a permanently implanted system without removing the distal end of the lead from the target location. In another aspect, the entire trial system can be disposable and replaced with a permanent lead and IPG. In one aspect, the EPG unit may be wirelessly controlled by a patient remote in a similar or identical manner as the IPG of a permanently implanted system would be. The physician may alter treatment provided by the EPG through use of a portable clinician unit and the treatments delivered are recorded on a memory of the device for use in determining a treatment suitable for use in a permanently implanted system. FIG. 3B illustrates an alternate configuration in which the lead 20 is connected to a lead extension 21 through a connector 21. This allows for the implanted lead to be used for both the trial and permanent system. This also allows the lead 20 of a length suitable for implantation in a permanent system to be used. Three access locations are shown: two percutaneous puncture sites, one for the lead implantation over the sacral area, and one for the extension exit site, while in between the puncture locations an incision (>1 cm) is made for the site of the connection of the lead 20 and the extension cable 22. This approach minimized movement of the implanted lead 20 during conversion of the trial system to a permanently implanted system. During conversion, the lead extension 22 can be removed along with the connector 21 and the implanted lead 20 attached to an IPG that is placed permanently implanted in a location at or near the site of the first percutaneous incision. In one aspect, the connector 21 may include a connector similar in design to the connector on the IPG. This allows the proximal end of the lead 20 to be coupled to the lead extension 22 through the connector 21 and easily detached and coupled to the IPG during conversion to a permanently implanted system. FIG. 3C illustrates a detailed view of an EPG patch adhered to the skin of the patient, an additional adherent patch 16 disposed over the percutaneous incision through the lead extends into the patient and another additional patch 16 covering a loop of excess lead, the patch overlapping the first additional patch and the edge of the EPG patch 10. This configuration is advantageous as it substantially covers and seals the EPG and the lead from contamination and prevents accidental disconnection or migration of the lead by the patient, and streamlines the external portions of the system so as to improve patient comfort and allow a patient's subjective experience to more closely match what the patient would experience in a permanently implanted system. FIGS. 4A-4C illustrates an overhead view and side views of an embodiment of EPG 40 that is smaller than a subsequently used IPG. Such an EPG can be situated within an EPG adherent patch affixation device 10, or in any any other affixation device described herein. In one aspect, the EPG is smaller than the IPG in the corresponding fully implantable permanent system. In certain embodiments, the outside width (w2) of the adherent patch 11 is between 2 and 5 inches, preferably about 2.5 inches, while the outside length (l2) of the patch 11 is between 3 and 6 inches, preferably about 4 inches; the width of the EPG (w1) is between 0.5 and 2 inches, preferably about 1 inch, while the length (l1) is between 1 and 3 inches, preferably about 2 inches; and the thickness (t) of the entire EPG patch 10 is less than 1 inches, preferably 0.8 inches or less. This design is considerably smaller than EPGs in conventional systems and thus interferes less with the daily activities of the patient during the trial period. The above described dimensions can be applicable to any of the embodiments described herein. Although in this embodiment, adherent patch 11 encapsulates the EPG within an interior cavity, it is appreciated that the EPG could be coupled with an adherent patch in any number of ways, including use of various coupling features. In some embodiments, the EPG is supported within a pouch of a belt or covered by an adhesive patch or surgical tape. In some embodiments, such as those described below, such coupling features can be configured to allow for ready removal of the EPG from the affixation device. The underside of the adherent patch affixation device 11 is covered with a skin-compatible adhesive. The adhesive surface may be configured with any adhesive or adherent material suitable for continuous adhesion to a patient for the direction of the trial period. For example, a breathable strip having skin-compatible adhesive would allow the patch 12 to remain attached to the patient continuously for over a week, typically two weeks to four weeks, or even longer. These aspects can be included on any of the affixation devices described herein that couple to the patient by means of an adhesive surface. FIG. 5 illustrates an example EPG 40 for use in a neurostimulation trial in accordance with various aspects of the invention. EPG 40 includes a substantially rigid outer shell or housing 41, in which is encased a stimulation pulse generator, a battery and associated circuitry. EPG 40 also includes a connector receptacle 42 accessed through an opening or port in the outer housing 41 and adapted to electrically connect with a proximal lead connector 24 of a neurostimulation lead 20′. Although EPG 40 is shown connected with neurostimulation lead 20′, lead 20, cables 22,26, and 27 may also be connected to EPG 40. Connector receptacle 42 includes multiple electrical contacts (e.g. six contact pins, eight-contacts pins), all or some of which can be connected to corresponding contacts points on a connector coupled thereto, depending on the type of connector. Connector receptacle 42 could be configured according to varying types of connector standards beyond that shown, for example, a USB or lightning cable connector. Lead connector 24 can include a proximal plug or boot 25 that sealingly engages the port when lead connector 24 is matingly connected within connector receptacle 42 to further secure the mated connectors and seal the port from intrusion of water, humidity or debris. Boot 25 can be formed of a pliable material, such as an elastomeric polymer material, that is fitting received within the port so as to provide ingress protection. In some embodiments, this configuration provides an ingress protection rating (IPR) is provided at IP24 or better. In this embodiment, connector receptacle 42 includes multiple electrical contacts, each operatively coupled with the stimulation pulse generator, so that the EPG can deliver neurostimulation pulses to multiple neurostimulation electrodes of the lead when coupled to the connector receptacle 42. In one aspect, EPG 40 is configured with a multi-purpose connector receptacle 24. For example, connector receptacle 42 can be coupled with either a neurostimulation lead 20′ as described above, or can be coupled with a power connector of a charging cord to allow recharging of an internal battery of EPG 40. Such a configuration is advantageous as it allows the EPG housing 41 to be designed with a single opening or access port, which further reduces the potential exposure of internal components to water and debris, since the port is sealingly occupied by the lead connector during delivery of therapy during the trial period. In contrast, a device having a separate charging port would likely either remain open or may require use of a removable plug or cover to seal the additional port. EPG 40 can further be configured with multiple operating modes, each mode suited for a different purpose for which connector receptacle 42 can be used. Such modes can include a therapy operating mode in which the stimulation pulse generator of EPG 40 delivers stimulation pulses to the neurostimulation lead connected to connector receptacle 24, and a charging mode in which a rechargeable battery within EPG 40 receives power. In some embodiments, EPG 40 includes only two operating modes, the therapy mode and charging mode. In other embodiments, EPG 40 can include various other operating modes, including but not limited to, various testing modes, a dual lead mode, a bipolar mode, and a monopolar mode. Such modes can correspond to differing connectors of a specialized cable set, such as any of those shown in FIG. 12B-12F. EPG 40 can further include an indicator 44, such as an LED, that indicates a status of the EPG 40, which can include an ON/OFF state, a hibernation state, a mode, or a charge state (e.g. “charging needed,” “low”, “fully charged”, “charging”). In some embodiments, indicator 44 is configured with differing colored LEDs that indicate differing states by displaying different colors. For example, a red light output can indicate “charging needed”, an orange light output can indicate “low” charge, and a green light output can indicate a “fully charged” status). Differing modes or status of EPG 40 could also be indicated by use of multiple lights or flashing or blinking patterns (e.g., flashing green indicates the EPG is “charging”). In another aspect, EPG 40 is designed as a substantially planar polygonal prism having parallel major surfaces that are positioned flat against the patient's body when affixed to the patient during the trial period, such as the rectangular prism shown in FIG. 5. In this embodiment, EPG 40 is a substantially rectangular shape with rounded corners and curved edges, the x-axis extending along a lengthwise direction of the rectangle, they-axis extending along a widthwise direction of the rectangle and the z-axis (not shown) extending along a thickness direction. As shown, the corners and edges are rounded or chamfered for improved patient comfort when worn against the patient's abdomen or on the patient's belt. While a substantially rectangular shape with rounded edges is depicted here, it is appreciated that EPG 40 can be formed in various other shapes (e.g. circular, triangular, square, symmetrical or non-symmetrical shapes), and still be suited for use with affixation devices according to the principles described herein. FIG. 6 shows a schematic of the example EPG 40 having a multi-purpose connector receptacle 42. EPG 40 includes the stimulation pulse generator 46 and rechargeable battery 48 each coupled to connector receptacle 42 via associated circuitry 47 that controls delivery of power to and from the rechargeable battery 48 and the stimulation pulse generator 46 and connector receptacle 42. Circuitry 47 can include one or more processors, controllers and a recordable memory having programmable instructions recorded thereon to effect control of the stimulation pulse generation, rechargeable battery discharge and charging, and indicator 44. In some embodiments, memory includes pre-programmable instructions configured to effect multiple different operating modes, for example the therapy mode and charging mode. In the therapy mode, circuitry 47 uses the rechargeable battery 48 to power the stimulation pulse generator 46, which produces stimulation pulses that are delivered to a connected neurostimulation lead via the connector receptacle 42. In the charging mode, circuitry 47 controls delivery of power delivered via the connector receptacle 42 to rechargeable battery 48. In some embodiments, circuitry 47 includes a controller that switches between differing modes, which can be effected upon connection of a certain connector types into connector receptacle 42. For example, in some embodiments, EPG 40 can include a detector that can detects a certain type of connector (e.g. lead connector, charging connector). In other embodiments, a connector type can be determined by measurement or detection of electrical characteristics of the
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