I came across this LiFePO4 battery system that seems intriguing. Does anyone have any experience with one of these? They can be connected serially or in parallel depending on what you are looking to do.
Here's a pretty decent video review of the lower aH version
[EDIT: I do see they offer a 10 year warranty which is nice, but if they're an unknown company, I'm not sur that adds too much piece of mind]