The battery bank is considered the heart of the off grid system, your solar energy is stored for use at a later time. SURRETTE/ROLLS is the Cadillac of lead acid solar batteries and are often seen in larger cooler climate off grid solar power systems. The smaller solar power systems often use DEKA absorbed glass mat batteries. The DEKA battery is ideal for remote location, where they charge slower and vent less hydrogen.
The battery bank in a off grid solar power system, is basically the heart of the system, it has to be there when the sun goes down, it is in essence the storage place of all the sunshine you collected. If you purchase properly designed solar batteries they will give you years of service. A poorly sized battery bank, and you will get years of frustration. You should get 10 or more years out of a properly sized solar battery bank.