Electronic – Replace a three wire tablet battery with a two wire one


I want to replace an old 300 mAh battery in my Chinese tablet with a new 3000 mAh one. The old battery has three wires: red, black and white. The white wire connects to a pad on tablet's mainboard labeled "T", which I have been told is used to connect to the temperature measuring thermistor built into the battery. However, the problem is that my new battery has only two wires: black and red. I connected the red and black wires of the new battery to plus and minus pads on the board and left the "T" pad unconnected.
The tablet works just fine with the new battery, but the problem is that I can not charge the new battery. I connected the charger for one hour but the battery charge level does not increase, not even by a percent.
I think this is because the "T" pad is not connected to battery. What can I do?

Best Answer

There is a convention that the "T" wire is connected to ground via a 10kOhm NTC, as mentioned for example on this thread on AnandTech. Replacing it with a 10k fixed resistor should enabling charging, but on your own risk. The sensor is used to prevent charging when the battery is too cold or too hot (possibly caused by environment temperature) to avoid damaging the battery. Also it can be used as an emergency cutoff if the battery gets too hot during charging. A fixed resistor will disable these safty functions.