For what are Li-ion battery second protection ICs necessary?
In what applications are they used?

Lithium-ion Battery Protection ICsHow to use

A Li-ion battery second protection IC has a overcharge detection function and can add sufficient redundancy and double protection to a normal battery protection circuit.
Our second protection ICs adopt a kind of fuse device called SC protector. The SC protector cuts off the current path and prevents overcharge by overcharge detection state continuing for a certain period of time. (Refer to the figure below)

Laptop PCs, electrical bicycles, and li-ion battery systems for back-up power supply have adopted second protection ICs to secure safety. Additionally, these days, other applications such as power tools and cordless cleaners have also come to use those ICs in order to meet needs for double protection required by laws and standards such as Electrical Appliance and Material Safety Act in Japan.