Have a cat 3126 powered toy that was setup to run 4 batts. Like many locals in the area, when the time comes, they don't buy the second pair as one pair usually can start them down to 10F or so. Anyway, I have a pair of group 31 on the 3126 that are getting weaker. Someone gave me a really nice pair of deep cycles, but they are crank rated to 700cca. I was surprised to see that on the batts. I am not ignorant to batt design and understanding. Just curious if anyone is doing this with success? I have not yet load tested my current batts to see how much they have, but seems like these others might run decent. Even better if I can get another pair like em and just run the factory 2S2P config.
Yes, it will work fine, down to who knows how cold, pretty close to as cold as starting type will start it. You're probably talking about marine cranking batteries with that rating. I'd be hesitant to mix old and new ones, even if they're only six months old and same brand. No need for four of them, one should start the little six anytime you want it to start without plugging it in.
I agree with Delmer about not mixing unmatched lead acid batteries in parallel. The weaker charges from the higher voltage battery, then the cycle reverses till both are dead.