Yes, protection of the batteries.
Instead of the protection circuit that we have to put inside the battery pack, we should also consider the protection that we locate external of the PCB.
The battery can itself be heated by certain reasons for instance may be there was overcharging activities and the protection circuit of the battery was not working, or the battery could be placed on the hot surface etc...
So, we must put extra protection on the battery itself to sense the high temperature and overcurrent if let say out protection circuit failed to protect the battery at the 1st place!
So, the concept of the physical arrangement of the protection components inside the battery that I wanna to do the analysis. haa...