rare on-board type. 12v 4200 mAh NiMH Works great!   https://www.ebay.com/itm/175804209569?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=kvs3HRKyRja&sssrc=2349624&ssuid=kvs3HRKyRja&var=&widget_ver=artemis&media=COPY