So, depending on the voltage of each battery and how you wire them together, any combination of Voltage and Current (amps) is possible. It's easy to remember the difference between series and parallel wiring.
In series the current (flow of electrons) can travel only 1 path. That is from one battery, through it, and then to the next and so on. The current remains the same but the voltage adds. A simple example of series wiring is a common flashlight.
In parallel, since all negative connections are together and all positive connections are together, the current can (and does) flow through multiples paths. The voltage remains the same but the current adds. An example of parallel wiring is jump starting a car battery with another car battery.
So, series wiring provides only 1 path, and parallel wiring provides multiple paths. To calculate the number of required batteries, use our System Sizing Tool. Also, the Example Wiring Diagrams will show where the batteries fit into the overall Solar Power System wiring.