Well the wall wart is 5.0V. I've charged off of a USB port which is also supposed to be 5.0V.

I have a solar panel that puts out 5.0V but it does it in bursts, on for 2 seconds, off for 3 seconds and that just puts the tablet into a mode where the screen is always on and it's playing sounds for the start charge event and it ends up discharging the battery.

Frank