Battery Management System (BMS)

A battery management system (BMS) is the controller inside a battery that measures cells, protects them, and publishes the charge and discharge limits the battery can safely accept.

The BMS lives with the cells. It measures cell voltages, temperatures, and current, balances the cells, estimates state of charge and state of health, and opens the contactors when a limit is crossed. It protects the battery; it does not decide when to use it. The energy management system asks for power and the BMS has the veto. A BMS always ships with the battery from its manufacturer and is never bought separately.