Check out electrobikeworld.com they are base in USA and do custom lithium ion battery packs. You can give them the dimensions, the specs and the cells you want and they can build it for you. I had them build me a 52v 30Ah with Panasonic GA cells and the price was cheapest I found anywhere! It even comes with a 5amp charger and 1 year warranty. I highly recommend them if you need affordable lithium batteries.