This is a great thread - Gave me some ideas with a Teclast p80x (8 inch tablet) that I have with a swollen battery.
Excuse the lack of proper electrical terms below - I have never been formally trained.
Mod: created a new thread

@Mods: I have added this here to this thread, to hopefully help others that come to this thread. If this should be somewhere else - either move it or tell me where I should put it.

I run a Home Assistant server and had been using this tablet as a wall mounted dashboard. Obviously I didn't need the battery as it's plugged in 100% of the time. (If power goes out - my Home Assistant server wouldn't be able to turn lights on off anyway, so table was useless even if it had a battery)

Battery in the tablet had 5 wires connected to the circuit board, 2 power (red), 2 ground (black) , and 1 data? (white)

1. I removed the battery, but left the battery circuit board (had to remove a bunch of tape, and cut spot welds to battery tabs.)
2. Plugged in tablet with USB A to USB C cable
3. Couldn't use a USB C to USB C - something special about these and the power management on the tablet main board. I could only ever find up to 0.1 volts anywhere on the board
4. Use a voltage meter to find 5 volts on the tablet main board
5. Connect wire from tablet main board 5 volts via diode (i had a spare 1N4007 available) to the +ve battery terminal on the battery circuit board (diode points toward battery circuit board - didn't want capacitor pushing any voltage back to tablet main board and diode usually rips out about 0.8 volts, so battery circuit board will only get about 4.2volts. i.e. same as orig battery)
6. Put ceramic 104 capacitor across +ve and -ve battery terminals on the battery circuit board

This worked - Using the normal tablet USB C charging port (with USB A to USB C cable)

1. Tablet booted.
2. Could log in, change settings etc.
3. Battery percentage shows 100% - Doesn't show its charging. (Doesn't bother me)
4. However, as soon as I tried to run any app that I expect drew too much peak current, the tablet would act if the (imaginary) battery had been disconnected and the power cable had been pulled out. I.e. back to pre boot up stage. i.e. it was off - not in standby.

So I upped the capacitor size - only one I had available was a 400v 10uF Aluminium Electrolytic.
Now it seems to be working no issues at all. Been running for about 16 hours as of this post.

Problem I have is the 400v 10uF cap is way too big to fit inside the tablet case, hence not able to mount back on the wall with my current mount.

So the question is:
How do I determine the correct size capacitor?

1. Ceramic 104 (0.2 uF) was too small.
2. Electrolytic 10uF 400V is too big.

As 10uF is working, can I just use a Tantalum 10uF 25V cap?
It's small enough form factor to fit inside the back case of the tablet (5mm by 3mm)

Thanks in advance for any responses.

 

Hey Folks - The "Thread" I refer to abaove is here: Using capacitors and a resistor to trick a tablet into booting off USB
Thanks to clifter1 for starting that thread, and all those who contributed.

Decided to give a Tantalum a go.
I was able to pick up a a few 10uF Tantalums today.
I have subsituted the 10uF 400v Electrolytic for a single 10uF 35V ($1.15 AUD) Tantalum.
Tested it - Seems to be working ace.
Soldered it all together and added heat shrink, and put the rear case back on.
It's working and back on the wall!
No case mods required.
No extra power supply required.
No battery.

It was going to cost me about $20 AUD for a battery (delivered - and not until March...) - and might only get another 2 years out of it.
Sorted, piecing togther a few youtube videos and the above thread, for a little time and about $3 worth of parts.

Love the internet!!!

If any of this has helped, pop a reply in down below.