Soo umm that can't be good...

[redshift]

Yep, too cold. You need to look into a heating pad or similar, and also find a way to insulate the batts, I use thin packing foam.

Packs preheated are crazy punchy and shouldn't puff due to low temp because they can't really cool back off as long as they start warm. You can't keep an eye on temps with hardcases and that's why I'd never run them. You really need to know what's going on with them during a run. If you sell them do yourself a huge favor and get noncased packs next time. The cases will do nothing to insulate them, and will contribute to overheating in the warmer months, double bad news.