When a battery is added to a solar pump kit, the pump will work at the battery voltage, such as 12v, instead of the higher solar panel voltage, such as 18v. Therefore, pump will run at a compromised performance with a battery, but for much longer hours on a daily basis.

Battery can store the surplus energy from the solar panel in the daytime and continue to run the pump after sunset, or run the pump on demand when sun light is no longer availabe.

On overcast days, the solar panel may not be powerful enough to run the pump all day long, but battery can accumulate the weak solar energy and release it when there is sufficient energy stored to run the pump for a few hours.