Long time ago i worked on pocket amplifier (old days when pocket mp3 players weren't obsolete), people we're designing really nice small amplifiers. Although i remember, that most of the time they recommended to use standard batteries instead of rechargeable - due to some kind of voltage stability and different audio sound on different SoC of accu (some kind of distortions, but harder to catch due to being stable at given SoC). How well your amplifier handle this? It's really cheap, and if it would be immune to voltage changes (our Li-Po provide very different voltage during discharging) it would be indeed great. I know it operates at vide variety of voltages, but doesn't it "calibrate" itself on start to given voltage, and voltage change during long playback will distort sound?