What Kind of Battery do I need? 

The most common type of battery used in a solar system is a lead-acid battery. They are generally used because they have a low initial cost and are readily available. These batteries must be deep-cycle batteries. If the battery is a shallow cycle or automotive type it will not function correctly in the system. The deep cycle batteries are designed to discharge and recharge or cycle day after day for years.

The next decision is whether the batteries are sealed or flooded. A sealed battery never needs water added nor does it need an equalization charge. The benefits of this battery are; the battery can be mounted in any position and are easy to transport. The one downside is that they need to be monitored closely as to not overcharge. A flooded battery also needs close attention. The water level needs to be checked often and re-filled. You will also need to perform an equalization charge, which is a long steady controlled overcharge. This removes sulfation from the battery plates. While this restores the battery's capacity, it can lessen the life of the batteries by warping the plates. 

So you need to decide which battery fits your specific needs. As long as the battery is taken care of you can expect a long battery life using either battery type.