Connect the two 36 voltage sources in parallel to obtain one 36v source with an ah capacity considerably greater than 5ah but probably less than 10 ah. Connect a separate identical set of three 12v 5ah batteries to create another 36 volt battery with 5 ah capacity.

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3 12 volt batteries in parallel. This can however be fairly easy to. Check that your battery charger is set for charging at 12 volts. But what happens if you wire batteries of different voltages and amp hour capacities together in parallel. They can have different capacities on account of size or age but the same chemistry eg. All flooded lead acid or all agm. A 6 volt battery might have a cell voltage of 22 volts and a 12 volt battery might have a cell voltage of 21 volts.
The reality is that no 6 volt battery is exactly 6 volts and no 12 volt battery is exactly 12 volts. Individual cell voltages differ even with batteries of the same brand and manufacturer. The process is simple but as the capacity of the batteries increases depending on the number of batteries wired in parallel it can take twice the time to charge two 12 volt batteries and three times as long for three batteries. The parallel connection of two identical batteries allows to get twice the capacity of the individual batteries keeping the same rated voltage. Four 12 volt 2000 mah wired in parallel can provide 12 volt 8000 mah 2000 mah x 4. Two 6 volt 45 ah batteries wired in parallel are capable of providing 6 volt 9 amp hours 45 ah 45 ah.
Following this example where there are two 12v 200ah batteries connected in parallel we will therefore have a voltage of 12v volts and a total capacity of 400ah ampere hour. How battery charging works with a parallel battery bank lets suppose you have 3 different 12v batteries wired in parallel to supply 12v power to your rv.