I see a lot of resistance here to a clear benefit for 12v versus 6v in two-battery configurations. Those who still need help with this, consider two hard drives configured in Raid 0 versus RAID 1. There is a benefit to redundancy.
We all agree batteries require proper maintainance--okay, I don't, I'd rather buy new batteries than ever endure the humiliation of checking SG. I water mine once a year, I buy new ones every four years, and since I have six batteries I have plenty of redundancy with my 6v GC-2s.
But if I only had two batteries, I would never chase the very slight price advantage of 6v GC-2s over the safety advantage of redundant 12v batteries, all other things being equal.
