Does the device/charger consume power after charging is complete? I'm a bit OCD about efficiency and I have noticed that at least one of my two Android devices tells me to unplug it after charging is complete to save energy. My questions are:


Is it true that a chargeable USB device may or will continue to consume similar amounts of power if it remains plugged in after fully charging?
Does this vary based on hardware and/or software (Is it possible my LG Optimus T phone continues to consume similar power after it is charged, but my Nexus 7 doesn't)?
If a device continues to "consume" power after it is charged, where does it go (laws of thermodynamics and all)?


In searching for my answer, I have found the following questions relevant but not entirely applicable to my question:


Does constant charging harm my Android cellphone?
AC-USB Charging Device Makes Sounds when Device Fully Charged
What component of my phone charger produces chirps and how does it do that?
Like any other device, regardless if the battery is full or need charging it consumes energy all the time. When your device is fully charged and still plugged in then the charger replenishes the energy used by the phone. It uses less energy than when charging but still. This is called Trickle charging
It is advised to unplug device because keeping you battery fully charged all the time will reduce its capacity and make your battery die faster. Battery needs to be partially discharged and then be fully charged on a semi-regular basis in order to prolong its life.

The following sentence is from  Article on prolonging battery life


  Let’s look at real-life situations and examine what stresses lithium-ion batteries encounter. Most packs last three to five years. Environmental conditions, and not cycling alone, are a key ingredient to longevity, and the worst situation is keeping a fully charged battery at elevated temperatures. This is the case when running a laptop off the power grid. Under these conditions, a battery will typically last for about two years, whether cycled or not. The pack does not die suddenly but will give lower runtimes with aging.


You can also read about partial discharging and charging here:

Techrepublic - Five tips for extending lithium-ion battery life