I almost exclusively use venom packs I have been phasing out my other brands and I have been quite happy with them. One is very very slightly puffed and all of them are treated the same I always balance charge them and storage em. I never run them longer than 8 minutes though, and I always charge at 6 amps. If your on the track for 15 min in 17.5 buggy you are stressing the battery. I'm not saying that's what's going on but just a thought.