A solar charge controller, also known as a charge regulator, is a voltage or current regulator that is designed to prevent batteries from overcharging. So if you have a 12 volt panel that is likely capable of outputting between 16-20 volts – understand that these numbers aren’t completely set in stone and that they are instead dependent on many other factors such as the position of the sun in the sky etc. So using a solar charge controller ensures that you won’t overcharge the battery – seeing as most batteries will require about 14-14.5