Although the control circuit of the controller varies in complexity depending on the PV system, the basic principle is the same. The diagram below shows the working principle of the most basic solar charge and discharge controller. Although the control circuit of the solar charge controllervaries in complexity depending on. According to the controller on the battery charging regulation principle, the commonly used charge controller can be divided into 3 types. 1. The most basic function of the solar charge controller is to control the battery voltage and turn on the circuit. In addition, it stops charging the battery when the battery voltage rises to a certain level. Older controllers.