I'll second ebikemarketplave.com. I have an Eflow E3 Nitro I bought used a four years ago assuming the battery was on its way out but at the right price. The battery lasted longer than I expected but it didn't survive my mistakes on last winter's less than perfect storage. EMP just replaced all of the cells upgraded from 10.8A to 15A for a very reasonable price. The bike is better than ever.