Whenever youhave a charging source (solar-electric system, or hydro, wind, or enginegenerator) connected to the batteries, controlling the rate of charge is vital.Solar charge controllers protect RE system batteries by managing the amount ofenergy the battery receives. Over discharging and undercharging can lead todecreased capacity, early failure, and replacement of an expensive component.Controllers adjust their behavior based on battery voltage. Besides managingthe current to the batteries, some controllers can act as load controllers,disconnecting DC loads if battery voltage gets too low. For wind and hydrosystems, with outputs that should not be turned off, some solar panel controllerscan be used as diversion controllers, sending excess power to a DC heatingelement instead of overcharging the batteries.