It's called a battery protector
Lithium battery protection board is mainly an integrated circuit board that protects against rechargeable (generally refers to lithium batteries). The reason why the lithium battery (rechargeable type) needs protection is determined by its own characteristics. Because the material of the lithium battery itself determines that it cannot be overcharged, overdischarged, overcurrent, short circuit and ultra-high temperature charge and discharge, the lithium battery lithium battery component will always follow a protection plate with sampling resistance and a current safety device
The protection board usually includes control IC, MOS switch, precision resistor and auxiliary device NTC, ID memory,PCB and so on. Among them, the control IC controls the MOS switch under normal conditions, so that the cell communicates with the external circuit, and when the cell voltage or circuit current exceeds the specified value, it immediately (tens of milliseconds) controls the MOS switch off to protect the safety of the cell.