Charging batteries with solar power is great on the environment and for batteries. Charging and maintaining batteries through solar will result in better battery performance and longer battery life. With solar chargers rated 15 watts or more, we recommend the use of a controller. It's no surprise that if a battery reaches full charge, but the sun keeps on shining, you risk overcharging the battery. Solar controllers regulate the voltage output from the solar panel and prevent batteries from being overcharged.
A charge controller, charge regulator or battery regulator limits the rate at which electric current is added to or drawn from electric batteries. It prevents overcharging and may protect against overvoltage, which can reduce battery performance or lifespan, and may pose a safety risk. It may also prevent completely draining ("deep discharging") a battery, or perform controlled discharges, depending on the battery technology, to protect battery life. The terms "charge controller" or "charge regulator" may refer to either a stand-alone device, or to control circuitry integrated within a battery pack, battery-powered device, or battery charger.
Renogy 30A PWM Charge Controller is a very nice controller, easy to install and very well made. It can be used with a 12V battery or battery bank.
Nominal Voltage: 12 VDC
Rated Charge Current: 30A
Working Temperature: -20°F - 113°F
Dimensions: 6.45 x 4.31 x 1.76 inches
Weight: 0.65 lbs