I'm thinking of redirecting the 5V+ and GND of the USB to a charger circuit (like Powerboost 1000) and a pack of LiPo batteries and build it into my keyboard (Kinesis Advantage, with lot's of free space inside). I also need to extend the push button and led(s) to somewhere on the back of the keyboard case.
user888Should be a simple project. You probably need a switch to disconnect the battery when not used. The BT-500 has an idle shutoff feature with configurable time length but it just shut itself off without disconnecting the power to the keyboard.