Using different "group size" batteries

[Seaotter]

I was wondering if there would be any issues in using two different group sized batteries together. Specifically, a group 31 and 4D. I thought I read that "group size" was just the exterior battery dimensions. Would the difference in amp hours be an issue as far as running or charging together? How about the stress on a F250 alternator especially with AGM's?

 

[sparky]

I don't know about any stress on the alt from AGM's, but the different group size batteries aren't going to affect anything. Optima's batteries are AGM, and I've used them in tons of boats, cars and trucks... never an issue with the alternator.