True deep cycle 12 volt batteries are few and far between. 6 volt golf cart batteries are relatively inexpensive and will outperform your typical 12 volt battery for the same footprint.
Dimensions are available on most battery manufacturers' web sites.
Charging times will be the same unless you go AGM which will charge faster if your charging system has the capability. Of course if you add more capacity, you can use more power which means a longer charge time.
If you don't have a multi stage charging converter, now is the time to do it. Your batteries will charge faster and last longer.
I converted over to 6 volt Lifeline AGMs (GPL-4CT) a year ago. They are awesome compared to the OE 12 volt group 24s that came with the RV. I also have a Progressive Dynamics multi stage converter.
The "best" batteries for lead are AGMs hands down and Lifeline is near the top of the AGM list (if not the top). Optimas (a popular automotive and marine AGM) aren't really suitable for RVs so pass on them. The down side? They cost me $600 for the pair.
