slo, Luna is the best that I've found, and since they're in the US, shipping is cheaper. The fact that no DIY company that I know of offers a warranty speaks volumes (TO ME). The OEM's like Haibike can offer a two year warranty on vehicles that will be used off road and BionX offers a three year warranty on their batteries (I think). Crap shoot with all of the DIY AFAICT.
Wouldn't even consider an ebay or "ali (baba or express)" battery.