Batteries are one of the most important components in an autonomous, but often neglected, solar system.
Some aspects to take into account:
Capacity of battery bank: Capacity is expressed in Wh = Voltage of module x Ah
Useful battery capacity: Never discharge more than 50% of the battery, and after discharge, it must be charged as soon as possible.
Number of discharge cycles at 50%: Sets the actual battery life. Often, in the battery catalogs, the manufacturer expresses the lifetime in years of the product. However, this lifetime reflects use in stand-by, or UPS, not in solar cyclic use.
For solar use, always check the curve of number of cycles, and always be suspicious of catalogs without this information, unfortunately more and more frequent from other companies, usually are UPS batteries, not solar batteries.