I can charge my M803/M702 (Revolver) battery using my "Universal USB charger" that I got from V4L. They're very inexpensive (under $10) and they don't have a
threaded receiver. Just a silicone "sleeve". They will charge just about anything... 510, 901, KR808D-1, M803/M702.. etc...
Other vendors carry the same charger.