Batteries

kaysdriver wrote:
My 21 foot TT came with a small deep cycle battery. My Problem is when I dry camp it doesn't last the night running my cpap machine. Cpap has a real low draw. I am going to install a 2 battery system. The question for me is 2 high capacity deep cycle batteries better than 2 900 cca regular batteries.

CPAP are not really "a real low draw" when you are talking about a small 12V battery. My wife's takes almost 100 watts A.C., I assume you have similar. Add 15% to allow for the efficiency converting to AC from the battery. As you have found that will pretty solidly drain a group 24 battery which only has something like 80 Amp hours capacity and you are taking about that much out if it's on for 8 hours at like 8 Amps draw. Double that as you don't want to draw most batteries down less than 50% and that is what you need for the CPAP alone. 130 AHs. This means with 2 standard 6V 'golf cart' batteries you should have enough to get through the day assuming reasonable other current draws, but you would be charging at least some every day as they don't like to get below 50%.
There is endless discussion about the best route to go for batteries. There is no best answer. the 6 volts are rugged, if cared for properly, but with only 2 if one fails you have nothing. They are likely the most cost effective if that is a criteria. I favour AGMs, for a couple of reasons but cost is not one since they are at least twice as much for a given capacity. They will charge much faster, take more abuse, and they are practically speaking sealed so no worry about watering or leaks.