A 4s lithium 18650 battery BMS packs PCB protection board is a small circuit board that is designed to protect the battery from various risks like overcharging.
The nominal voltage of the 18650 Lithium Ion battery is 3.6 volts. However, when fully charged, the voltage can range from 4.2 to 4.35 volts, depending on the specific type and model of the battery.
