A lithium battery pack needs multiple layers of protection. A battery management system (BMS) monitors operating conditions such as cell voltage, current and temperature. Depending on its design, it can limit or stop charging and discharging outside allowed ranges and help keep cells balanced.
A correctly selected circuit breaker serves a different purpose: it can physically interrupt a circuit during an overcurrent or short-circuit fault. The BMS and breaker complement each other; neither eliminates every safety risk. Cell design, cable sizing, installation and periodic inspection still matter.
SmartPropel battery cutaway from the homepage requirements workbook.