The main function of a charge controller is to regulate the charge and discharge of single batteries or battery banks. Besides this primary function, charge controllers often offer other features such as, metering and data logging, low battery disconnect, and built-in lights control to turn lights on and off during the night. Charge controllers can be found in sizes ranging from 4 to 80 amperes and nominal voltages of 12, 24 and 48 volts. The simpler and more inexpensive charge controllers stop the charge of the batteries when they are full and will resume charging when the batteries reach below a preset voltage. Pulse Width Modulated (PWM) charge controllers turn on and off very rapidly; holding the batteries fully charged and making better use of available power. Maximum Power Point Tracking (MPPT) charge controllers can find the point in which the source can deliver power most efficiently, and then charge the batteries. MPPT charge controllers are normally used in larger arrays; they also allow the use of modules with higher rated voltage. MPPT controllers cost more than other charge controllers but can deliver up to 30% more charging capacity from the solar panels to the battery bank.