Shouldn't charge or store batteries in your mod, nor charge while unattended for a long period of time, aka overnight. Might as well not buy batteries in the dollar store or on eBay. Don't use batteries that are already damaged, or have peeled off wrappers etc. Batteries are married, meaning if you have a 2 - 4 battery mod, make sure they are all the same brand, amps and drainage. Never for example use these batteries in different mods and then mix and match them as you please, specially if one is at a different charge etc. Some have overcharge or/and drainage protection but not all of them.
So to answer your question since we have barely any information that could indicate any user error or manufacturing defect, i would recommend taking it back to the shop or contact the warranty department and have them sort it out. Unless its user error, then you should make some changes going forward. Either way, its unsafe in my personal opinion.