What is the Voltage on a tablet's battery when it is turned off

Question

Basically I tried to find out what's wrong with my broken tablet, so I used a multimeter to measure the voltage at the battery pins on the tablet's board and it was 0.1 roughly, and the transistors had some voltage on them, but the device was not booting. So the obvious reaction was to cut out the old 2x3.7V in series battery and try to use a normal 9v battery(through the battery protection). The screen what reacting this time but the OS was not, and the voltage on ports was half of that of the battery.

So the question is why there was only 0.1V at the beginning. Maybe the 2x3.7V battery was not charged enough?

Also if the battery used was 9v,it could activate the screen but not some other components?

Answer 1

Those 3.7 V batteries need to have a voltage between 2.5 V and 4.5 V per cell, if they're outside that range then consider them to be damaged. Some cells might survive a short time below 2.5 V. But 0.1 V means that they're dead.

9 V might be on the edge of what a device that is supposed to work on 2 Lithium based cells in series can handle. Chances are that a 9 V battery is unable to deliver enough current to start the tablet. So the tablet will attempt to start but as soon as it switches on any part which consumes a lot of current (for example the backlight) the voltage will drop (due to the high internal resistance of a 9 V battery) and the device will reset.