6V vs. 12V Ah equal?

Huntindog wrote:
The problem is that 12 volt batteries are often rare, heavy, and/or expensive.

Here's one in Group 29/31 size ... the last model at the bottom of the chart:

http://www.interstatebatteries.com/cs_eStore/content/product_info/wheelchair_spec.asp

I use two of them in our Class C for a total capacity of 200 amp hours. I maintain them with the stock Parallax 13.8 volt converter and the Ford's 130 amp alternator. The label on the top of the batteries says their float voltage range is 13.5 to 13.8 volts, so most of the time they get floated and charged within the same voltage range (the converter's average range). They've been in the rig now for around 6 1/2 years and are still going strong, but as Huntindog stated - they don't give them away. You never regret buying quality ... you just have to figure out how to first pay for it and then how to take care of it so it lasts.