The previous poster mentioned a schematic without showing. If you need to get this battery up above the charge % barrier you can bypass the pcb. I am wording this for those with tech knowledge and those without, for understanding voltages, finding polarities and phone disassembly please google it, I took the time to do this likely for just a few people to be able to boot up their old tablet for a spare or to get pictures they thought lost, without spending more than tablet value on a battery.
*****please note that since the following is bypassing the protective safeguards and while I view it to be safe, it may void warranties or although highly unlikely could damage the battery or cause a fire. So for my conscience and in case of unknown variables please do this while babysitting the phone, with it on a non flammable surface and fire extinguisher ready. "That's an adequate disclaimer right?"
Pop the back cover off, unscrew the two small Phillips screws, drop out the battery and peel back the tape covering the pcb......you will see 2 rows of 4 gold contacts which in theory could be used to charge from, however with such small contacts and inability to find out if one of the POS contacts could be overcharged, the average person would have difficulty clipping onto these without risking contacts touching.
My fix, take an exacto and cut the safety tape around the pcb until you get to the two silver leads from the pcb going to the battery itsself, mine read under 1.5v at this point and barely anything at the double quad gold points I mentioned. Although it would technically handle 5v or more, "your car battery is 12v and runs at 14+ regularly" find an old plug style wall charger "easy to attach to a basic male female plug, from lots of old chargers, "or just cut the head off any old phone wall charger if you know to find the + -. definitely below 1000ma 3.7v-4.2v for safety, I chose a 500ma 4.2v ."check voltages if possible in case it is higher than listed" Typically the outer shaft of a male plug is the - and the inner is the + .
The positive battery lead is on the left and the neg is the right, if looking down at the terminal/circuit side of the pcb on top and facing you, the neg is almost dead center of the circuit board to clear any confusion.
Run 2 leads from the 3.7-4.2v charger to the +- battery leads for an hour, retape the protection board and reinstall. If you have a meter, check voltages, try to get it close to the 3.7 but it should turn on with less, 3.7v lithium batteries off of charge are generally safe holding up to 4.2 from my experience btw.
I hope this helped or at least saved someone money " I hate buying $50 worth of parts to fix a $50 item just to retrieve a few files.