It wouldn't be a deal breaker for me.
6 volt battery is comprised of 3 cells. 12 volt battery has 6 cells. If they weigh the same and are all deep cycle batteries then they'll perform about the same.
In the past, 6 volt batteries tended to be true deep cycle batteries. Bigger and heavier. They were compared to lighter marine type batteries.
When it comes to batteries, the biggest and heaviest is often the best! http://www.classbforum.com/phpBB2/vi...=9&t=344&p=602
Looks like the Group 31 SunXtender PVX-2560T weighs 75 lbs and the Lifeline GPL-31XT weighs weighs 74 lbs. I'd expect very similar performance from them.
I'd love to hear opinions on this. I like to learn.