A charge controller maintains the life of the battery by protecting it from overcharging. When your battery has reached a 100% state of charge, the controller prevents overcharging by limiting the current flowing into the batteries. Pulse width modulated (PWM) charging, 3 battery charging profiles, improved 4-stage charging, and Maximum Power Boost, for topping up batteries at the end of daylight. LCD digital display shows solar array charge current, system battery voltage and battery capacity. Built-in USB charge port.