What is the difference between: No protection, PCM or BMS?

Depending on a lithium batteries chemistry will depend on how sensitive that chemistry is to catastrophic events. For instance, LiPo pouch models are susceptible to damage and subsequent catastrophic events, while LiFePO4 chemistries are very safe and do not have a fire hazard until the battery is above 800ºC. The other lithium chemistries fall in between these two extremes.

To improve safety and increase battery lifetime, manufacturers have introduced ways to protect the battery and the system. There are three basic approaches to lithium battery safety and control:

No built in protection
Protection Circuit Module (PCM)
Battery Management System (BMS)

Each approach is specific to markets and product needs.