PCM stands for Protection Circuit Module, which is a circuit device that protects Li-Ion Battery Packs so they can be used safely. This circuit protects the Li-Ion battery against heat, explosion, and ignition by limiting the voltage and current for charging and discharging.

The Li-Ion batteries currently being used have the advantage that they can be used for extended periods after charging and have sufficient capacity. However, the risk of explosion when the temperature rises is very high due to the liquid electrolytes they use, which are vulnerable to heat. Since they are more dangerous than other batteries, a protection circuit is a must to maintain battery performance and safety.