How do i build a battery charge circuit that doesnt require the battery to be disconnected
You can connect multiple charging sources to the battery using isolating diodes, which prevent current from back-feeding into lower voltage sources. Then you just need to make sure that the combined charging current does not exceed the the battery's rating.  

For the mains charger a simple DC power supply and series resistor will do the job. A 7 cell "8.4V" NiMH battery charges up to about 10.5V at the 10 hour rate (200mA for a 2000mAh battery) so you will need at least 12V to maintain a reasonably constant charging current through the resistor and diode.

This circuit shows how it could all be connected:-







simulate this circuit &ndash; Schematic created using CircuitLab

Note: most AA NiMH cells are only good for about 2~3A max. 4 servos alone could draw up to 2A, and the motors may draw a lot more. If you must use AA cells then I recommend Sanyo Eneloops. They have a higher discharge current rating than most high capacity NiMH cells, and hold their charge for much longer.