I am running nearly the same motor, I have the bd36, on a 36v 20 ah battery bought from Li Ping. pingping227 on ebay. Its just about a perfect setup, right down to the fit in the battery bag. Ping is the only "duct tape battery" seller on ebay that has won the trust of this group. So the problem is how to win one of Pings auctions? No problem. Just email him at the address in his ad, and talk to him. Dealing direct may even get you a lower price, but normaly you will wait a bit longer for delivery. Essentially it's treated like a custom order. You will love the light weight, long ride, and no need to worry about charging right away if it's not convenient. No voltage sag means your battery will never be lower than about 40 volts, so it may even be a tad faster than the sla's and a lot faster at the end of a long ride. My bd motor is faster and more of a watt hog than yours, but I can still go 20 miles at 25mph with this battery. You should get further at 20 mph. Get the 20 ah sise, its worth it to not worry about running out, and the slower drain will make it last it's maximum. One thing about these batteries though, you will need to build some kind of box or something for some extra protection in a crash or just the bike falling off the stand. Even just some extra cardboard in the bag to cover the corners if they get bashed. I used an aluminum baking sheet cut and folded to box mine. Saved it when I crashed! I have 1200 trouble free miles on mine, unless you count a few times I didn't let it charge long enough.