T-pin is used to connect negative coefficient thermistor (generally 10K) in early mobile phone batteries, which is directly connected to the ground of battery protection board, and has nothing to do with battery protection circuit. The function of the original design is to calculate the battery power through the change of battery temperature (the charging and discharging of lithium battery is related to the temperature), which leads to the change of thermistor (the higher the temperature, the smaller the resistance), so as to better carry out.

Some early batteries also had a D pin, which was usually connected to a common patch resistor. Motorola's mobile phone is generally connected to an identification IC, and this pin is basically directly grounded to identify whether the battery is correct. This needle is basically not needed for mobile phone batteries now.

At present, the T-pin of the battery is usually directly grounded with a patch resistor, and the resistance value is nothing more than 10K- 100K.

It is useless if this foot is charged with a universal charger, but you can't recognize it with the original charger, which means that your original charger has such an identification item, and the charger is relatively high-grade, with at least one comparison circuit.

The following is a schematic diagram of the mobile phone battery protection board. I don't know if you can understand. Note that the resistor on the T pin is directly connected to the battery ground.