It is the only Battery I can find on the market to fit in with mine.
http://www.aliexpress.com/store/product/500W-electric-bike-battery-36v-9ah-lithium-battery-with-pvc-case-15A-BMS-42V-2A-charger/131510_32462900649.html
http://www.aliexpress.com/store/product/500W-electric-bike-battery-36v-9ah-lithium-battery-with-pvc-case-15A-BMS-42V-2A-charger/131510_32462900649.html