Yep, they're lipos. I was initially concerned about (and prepared for) the cells being damaged, but the boots stayed rigid enough for it not to be a problem. They had a lot of wear on the Playa last year were fine. I did have a small issue with one of the packs expanding a bit. This year I'm going to take one cell out of each 'boot pack' to reduce weight and add some wiggle room.That's pretty clever! Are those flat lithium cells? I stuck a bunch of LEDs in the bottom of some platform boots last year and the abuse from walking around on them broke all the wiring connections by the end of the week (even though they were fully encased in shoe-goop). Hope that stays working for you, and we that both steer clear of the lithium horror stories I hear.
You're right, lipo's need to be treated with respect to avoid horror stories... especially when charging in the heat of the day. Like anything though, it's safe if you do it right
Great coat pics by the way!