Lead-Acid Batteries can safely be connected in parallel, provided they all have the same state of charge. So you should make sure that each of your parallel banks is fully charged before connecting them together. It doesn't matter if the parallel banks don't all have the same capacity, as they will share the load accordingly.
However, the voltage of each battery remains the same. Here’s what you need to know about connecting batteries in parallel: When you connect batteries in parallel, you connect the positive terminal of one battery to the positive terminal of the other battery and the negative terminal of one battery to the negative terminal of the other battery.
Connecting batteries in Parallel is normally performed to increases capacity. This can be done by connecting the positive terminal of the first battery to the positive terminal of the second battery. Likewise, the negative terminal of the first battery is connected to the negative terminal of the second battery.
Battery cells can be connected in series, in parallel and as well as a mixture of both the series and parallel. In a series battery, the positive terminal of one cell is connected to the negative terminal of the next cell.
In general, it is best to connect batteries in series because this increases the voltage while keeping the current the same. However, there are some advantages to connecting batteries in parallel. For example, if you want to increase the current without changing the voltage, then connecting batteries in parallel is the way to go.
These combinations are also referred as parallel batteries. If emf of each cell is identical, then the emf of the battery combined by n numbers of cells connected in parallel, is equal to the emf of each cell. The resultant internal resistance of the combination is,