I'm in favor of EarthX as well! They use real A123 cells, sturdy cases, and their protection circuits do everything they should do.
(EarthX or finding real A123 cells somewhere and piecing together a battery yourself. I tried A123RC.com - they work fine for my DRZ but they aren't A123 cells and don't have the starting oomph of full-blown cells. The guys dug up some very nice looking screw-terminal cells in a thread somewhere - bushmechanic and berglsmerg got some iirc.)