I can say for sure ('cause I was at the ROAR nats and saw it) that those blue things are two LiPo battery packs wired in parallel. They were running two packs for two reasons: First, to make sure they didn't dump over the 20 minute race, as a single battery they were running would last ~15 minutes. Second, for weight. The LiPo packs are so much lighter than regular NiMH batteries, they really changed the way the car/truck handled. Two 3200 MaH LiPo batteries from Orion weigh a combined 13.2 oz (
http://www.teamorion.com/Products/Batteries/Li-Po), which is fairly close to a six cell NiMH pack, at around 14 oz.