Solar power backup systems are a very important part of a residential solar energy system. If you intend to use electricity after your solar panels quit producing it, when the sun sets, you will need some form of backup. The most common solar power backup systems for electricity are batteries.
The most common battery used for residential solar systems is the deep cycle battery. Deep cycle batteries are similar to car batteries but are made to be able to discharge deeply and recharge slowly. Car batteries are made to discharge just enough to start your car and then be recharged quickly and would not last long at all. A deep cycle battery can last anywhere from four to ten years.
And of course there are several battery options available for use on your solar power system. There are two divisions of deep cycle batteries used in residential solar energy systems. The two divisions are flooded and sealed.
Flooded - these batteries use a liquid electrolyte, any substance containing free ions that make the substance electrically conductive, and have ports that can be opened and closed to be able to add more electrolyte if necessary. These are usually the cheapest, and longest lasting batteries. However they probably require the most maintenance as they tend to lose fluids as gases as the batteries are recharged. After a while distilled water needs to be added to the batteries.
Sealed - these batteries do not use a liquid electrolyte but use a gel electrolyte or Absorbed Glass Mat where the electrolyte is being held in glass mats. They are more expensive than flooded lead acid batteries and don't last quite as long. However they do have some advantages. Since they are sealed and don't require maintenance they can be stacked and stored on their sides and even upside down. That's great if you don't have a lot of room for battery storage. And since they don't require maintenance they can be used in remote locations.