Out of curiosity, what's your gearing? It's interesting that Brian admits there's a climate related issue with some packs. All I can say is, I live on a hot, humid, tropical island where its 90+ in the day for 10 months of the year, and nothing like that has happened to my Zippys. On the other hand, I do have a 6 cell NiMh SMC pack which can barely power my Scaler Baja. Lets hope your new packs are reliable.