Looking for Battery experts

I have a need to run a 24 volt start for my rzr.

I am looking for actual knowledge on batteries. Please keep speculation to a minimum. Really trying not to offend anyone, but my bottom line is getting thin and I would like to stay married a bit longer. LOL

Can someone confirm that when wiring the battery in series, should the batteries both be of the same amperage?

Any literature would be nice as well. Still googling, but have only found how to hook them up, I know how that works. And everything else that seems to have details is on hooking up batteries in parallel and that they should be the same size/age/capacity.

So why am I asking, well I keep melting the second battery, I am speculating because I had it as the smaller amperage battery.