Charge Controller

Since the brighter the sunlight, the more voltage the solar cells produce, the excessive voltage could damage the batteries. A charge controller is used to maintain the proper charging voltage on the batteries. A solar panel just performs under the parameters upon which it was built. It’s the charge controller, sometimes called a charge regulator that sites between the solar panel and the battery that regulates the voltage and the current and essentially halts charging activity temporally when necessary.
Solar panels are connected to the charge controller. The charge controller is connected to the battery.the solar electrical charge controller controls the incoming charge to the battery. More complex sophisticated charge controllers do even more. Your system cannot function without one. Any battery being charged, even with a small solar panel, can be over charged and destroyed given enough time without a charge controller.