Very interesting indeed, which type of touchstone are you using? TouchPad or Pre?

As a TouchPad and TP touchstone owner, I have learned that USB charging is considerably faster than the touchstone, however it is designed to be left standing on charge throughout the day. The Touchpad will also activate its charge cycle once battery drops below 95% charge.

I can't speak for any of the pre stones tbh, so I don't know if they have different voltages to compensate for varying batteries?

Just another thought.. This little project of yours would also open the doors for various Exhibition mode apps too.