What type of batteries are there?
The two major construction types of deep cycle batteries are flooded lead acid and Valve Regulated Lead Acid. Flooded lead acid batteries are the most common type and come in two styles. Serviceable with removable caps so you can inspect and perform maintenance or the maintenance free type.
In VRLA batteries, the electrolyte is suspended in either a gel or a fiberglass-mat. Gel cell batteries use battery acid in the form of a gel. They are leak proof and because of this, they work well for marine applications. There are several disadvantages to gel cell batteries for RV applications. Most importantly, they must be charged at a slower rate and a lower voltage than flooded cell batteries. Any overcharging can cause permanent damage to the cells.
Absorbed Glass Mat, or AGM Technology, uses a fibrous mat between the plates, which is 90 percent soaked in electrolyte. They are more expensive than a standard deep cycle battery but they have some advantages. They can be charged the same as a standard lead acid battery, they don’t loose any water, they can’t leak, they are virtually maintenance free and they are almost impossible to freeze.