[BrianG]

Yeah, I use a 14 cell pack right now. Feels heavy in your hand! I just basically take two 7 cell packs and lay them on top of each other and then heatshrink the whole thing. And with an even number of cells, the + and - wire come out the same end of the pack for the shortest wire run.

When I built my pack, I used a piece of thin hobby foam between the two layers. With all the vibration and impacts, I thought the label on each cell may wear away shorting out (the thin plastic label is the only thing insulating the whole outside can - which is the - terminal). The foam help cushion the cells a bit and also acts to insulate them if the label gets worn. I also put some double thickness noteboook paper between each cell for the same reason.