That would be me
Its actually an F3. The pack is NiMh rechargeable 12v at 9Ah.
There are 20 GP 18670 (450LAH) 1.2v 4500mAh cells in the pack. They have achieved the 12v using 10 cells in series and the 9 Ah by paralleling two sets of 10.
As you can see from the photos there is a hexagon stack of cells, three high. This uses 18 cells - the other two are in the middle with positive ends at the top and bottom of the pack. Negative from each set of ten is wired from the negative of these middle cells. The positive is bridged off to one of the side stacks where it goes up, down and up again before being wired off the tenth cell in series.
The wires from both 10 cell series are simply joined to a pair of wires that come out of the shrink wrap.
In the end, rather than getting it done commercially, I took a poster's advice and made a spot welder for the nickel tags like this
philpem.me.uk :: electronics :: welder
For a few hours of enjoyable messing about I now get over three hours of light sabre action from my Greenforce.