Hmmm... My packs all just use shrinkwrap to isolate the cells from eachother. My packs don't get too warm though as I usually run more cells / less current to keep heat down somewhat. If you're really pushing them something else as a spacer might be good, but it seems like the cardboard sleeves would hold in heat too much in that case.
I'm pretty sure the original A123 cells had cardboard sleeves and no shrink, then the switched to just shrinkwrap versions. If your packs are getting so hot that the shrink melts off then the batteries are probably overtaxed too. Of course there's always extra current draw caused by combat damage that's hard to adjust for.
Lucas, what size/shape packs are you making, and for what size bot? I can't tell from your description, are you talking about isolating the battery bars from the cell cans for the button ends with servo tape? I have messed up when soldering battery bars on a couple of times and melted through the shrink there. Not my best day building bots - I don't recommend it
Edit: though, on the up side, there wasn't a giant fire ball like there would be if I did something silly like that to a lipo pack.
-Zac
