Originally Posted by Surveyor Mike
I was under the impression that a marine/RV batt. was a deep cycle?
That's a common impression. A marine is somewhere between a true deep cycle with solid lead plates and a starting battery, which has a lot of thin plates.
has a great detailed explanation.
But, you asked for a simple suggestion, and I would go with a group 27 deep cycle.
A deep cycle as it will last longer than a marine. A group 27 will give you about 25% more capacity.
If unsure between two batteries in the same type and group; buy the one that's heavier.