A charge controller is basically a voltage or current regulator that keeps batteries from overcharging. It regulates the voltage and current coming from the solar panels going to the battery. Most “12volt” panels put out about 16 to 20 volts, so if there is no regulation, the batteries will be damaged from overcharging. Most batteries need around 14 to 14.5 volts to get fully charged.
A charge controller limits the rate at which electric current is added to or drawn from electric batteries. It prevents overcharging and may prevent against over voltage, which can reduce battery performance or lifespan, and may pose a safety risk. It may also prevent completely draining a battery, or perform controlled discharges, depending on the battery technology, to protect battery life. The term “charge controller” may refer to either a stand-alone device, or to control circuitry integrated within a battery pack or battery recharger.