Multiple Batteries in Parallel

Not sure what would be right with those two. Normally you want a sustained draw (not a flash draw like starting the car) to be no more than about 25% of AH capacity. With these you could perhaps go by RC or CCA if no AH spec, to get the proportion each will do.

So say the little one is half the other so it gets 1/3 of the action. Now check the little one's specs and see if that 1/3 of whatever the action is, is more than 25% draw.