Charge Preserver (eu.thedarken.cp) on Google Play
It's not pretty, but free and does its job.It will enable airplane mode when running on battery, thus disabling all wireless connection to achieve minimal battery drain.If a charger is plugged in, either usb or ac, it will turn airplane mode off and the previously active connections (wifi,3G,gps,etc.) will be restored.This app was a request by a user on XDA-Developers who wanted to use it on an android device he keeps permanently in his car.When the ignition is off, the device won't be charged and tries to conserve as much power as possible.When the ignition is on, the device will be charged and turn power conserving measures off again.Just thought i would share it :-).