While most manufacturers state not to install more than 4 strings of paralleled batteries, it is possible to have more strings in parallel without reducing the life of the battery or the batteries getting out of balance.
If these requirements are fulfilled, paralleling of up to 10 strings is possible:
The same voltage drops must be realized from each string to the end connection (load and ground) regardless if the string consists of one unit (single cell or monobloc) or several units
The performance data of all of the batteries has to be applied to the end terminal of each string. By using this parallel string configuration the reliability of the system is increased due to the redundancy. Neither battery life or reliability will be affected if this form of paralleling is done correctly. Parallel connection of strings with different capacities as well as different ages is possible (the age and capacity of the batteries within each string should be the same). The current during both discharge and charge will be split according to the capacity or age of the batteries respectively. Also, the type of lead-acid batteries may differ as long as the required charging regime and voltage (Vpc) per string is guaranteed.
Always connect the individual series strings first and then check that the different strings are at the same potential before connecting them together.