Battery management systems are electronic devices which manage and protect rechargeable batteries. Functions include:  Protecting the battery from overcharge (over-voltage and over-current),  Maintaining a battery at optimum charge,  Monitoring the battery for faults or conditions that could damage the battery (over-temperature for example),  Protecting the battery from undercharge, and  Protecting the voltage source (starting battery in vehicle) from being drained, by isolating the incoming power supply once it gets below a certain voltage.