To configure batteries with a series connection each battery must have the same voltage and capacity rating, or you can potentially damage the batteries. For example you can connect two 6Volt 10Ah batteries together in series but you can not connect one 6V 10Ah battery with one 12V 10Ah battery.
Understanding the series battery connection diagram: The series battery connection diagram typically shows the individual batteries and their terminals, as well as the connections between them. It may also provide information on the total voltage and capacity of the connected 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.
Connecting two or more sets of batteries together by wiring them in a series-parallel connection will increase both the voltage and capacity of the battery bank. For example, if you have 6V 215Ah batteries in a series-parallel connection, you can end up with a battery voltage of 12V and 645Ah.
If we want to have some terminal voltage other than these standard ones, then series or parallel combination of the batteries should be done. One more reason for connecting the batteries in series or parallel is to increase the terminal voltage and current sourcing capacity respectively. Connection diagram : Figure 1.
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.