This popped up on Facebook and I had to borrow it. When combining batteries to get to the right voltage to store your solar power, this is how it is done. Do it wrong and you get a flash of light, flying beads of molten metal and possibly worse. Just make sure all the batteries in a series string have the same amp-hour (AH) rating.
One thing to add is how the AH ratings work out. If the 6v batteries a rated at 200AH, then in the top illustration you will end up with a 200AH bank at 24V. In the second illustration, if 100AH batteries are all in parallel, then you have a 400AH bank. In the final illustration it combines the principles and each of the two series strings have 200AH or a total of 400AH at 12v.
In my home system, 2V cells, 6V batteries, 12V batteries and 18V batteries combine to make 48V at…well, I’ve lost track, but around 2000+AH, –Neal