In a 12v system, multiple batteries can be arranged in a connection or string called paralleling. This means that multiple batteries are connected to increase the total amperage pool or amp hours available to the system. This is used to allow the electronics run for a longer period of time without the need of recharging the batteries. Here is a diagram showing a parallel connection of two 12v batteries.

In other cases, multiple batteries can be connected in Series. The Series portion refers to multiple batteries connected in a line end to end to increase the voltage available. Two 12v batteries connected in Series end up outputting more voltage (12V + 12V = 24V). Here is a diagram of a Series connection.

Another style is called Series/ Parallel. This allows the total voltage and total amperage to be increased. (12V + 12V = 24V and 6A + 6A = 12A). Here is a diagram showing multiple batteries connected in a Series/Parallel connection.