I used a Mobee Power Bar to save money and the environment by not needing any batteries for Apple’s Magic Track Pad. I use in plugged in all the time, meaning that I never run out.
However this does eventually kill the rechargeable batteries inside, and meant mine would keep losing the bluetooth connection and need to be re-paired. Anyway, had a thought the other day and unscrewed it and used a spudger to prize it open gently. Its basically two AAA NiMH batteries inside a AA case. I replaced the AAA with new ones, and things seem to be fine again.