When batteries are connected in series, the voltages of the individual batteries add up, resulting in a higher overall voltage. For example, if two 6-volt batteries are connected in series, the total voltage would be 12 volts. Effects of Series Connections on Current In a series connection, the current remains constant throughout the batteries.
Simply, connect both of the batteries in series where you will get 24V and the same ampere hour rating i.e. 200Ah. Keep in mind that battery discharge slowly in series connection as compared to parallel batteries connection. You can do it with any number of batteries i.e. to get 36V, 48V, 72V DC and so on by connecting batteries in series.
There are two ways to wire batteries together, parallel and series. The illustrations below show how these set wiring variations can produce different voltage and amp hour outputs. In the graphics we’ve used sealed lead acid batteries but the concepts of how units are connected is true of all battery types.
The first thing you need to know is that there are three primary ways to successfully connect batteries: The first is via a series connection, the second is called a parallel connection, and the third option is a combination of the two called a series-parallel connection.
Most of the current will therefore travel through the bottom battery. And only a small amount of current will travel through the top battery. The correct way of connecting multiple batteries in parallel is to ensure that the total path of the current in and out of each battery is equal.
Batteries connected in series must have the same voltage and capacity ratings. Connect in parallel - Connecting two or more batteries together in parallel will increase the overall capacity. For example, if you connect two 12V 90Ah batteries in parallel, you will have a battery voltage of 12V and a capacity of 180Ah.