I bought a couple of Tenergy's on Amazon for $18 each, shipped.... 3 cell(11.1v), 20C size, 1000 mAh. Don't remember the length, but the depth and width were 16mm x 16mm. These fit slightly snug without the oring. I also found 1 in a Paintball store for $23. They are used for RC stuff, also. The factory batteries are 800 mAh and slightly smaller in depth. I also picked up an equalizing charger($35) but found it will NOT work without the HP leads so had to keep a little stub on the batteries that I cover with shrink tube and just slip it off to hook up the equalizer. They are the same on the RW and DW.
The GCU 1 batteries are 2 cell, 7.4 v.
Bob