Charging issues

I have the Magellan Yamaha Adventure Pro that came with my Rmax1000.   Took it out of the machine to charge it in the house via my computer, and when I power it off prior to charging, it turns back on the minute it gets plugged in.   You cannot turn this thing off.  And also, how long is it supposed to take for this thing to charge?  I plugged it in to my USB on computer before bed and upon waking, it was only on 8%.   I left it plugged in, and at 2 pm it was only on 30%.  Well at 7 pm, I go to check it and it was showing 0%.   How the heck does it go from 8-30% only to go back to 0%.    This is the most frustrating tablet that I have ever seen.   Not to mention that everytime you turn the key switch on in the machine, it boots back up and selecting the button for not continuing on battery power when you turn off your sxs does not power off the tablet.  You have to go back and hold down the red power button to get the option to power off.  Can something be done about this please.   Aside from keeping track of where you go and basic stuff like the camera, it's pretty much useless to think it's supposed to be an offroad tablet with trails.   Thanks Flea