I had a new battery "installed" for free from Sam's club 2 winters ago when it was bitter cold. Went out to start my car the next day at work and it was dead...no clicking, no nothing, lights off entirely. Got a jump and let it charge on the jumpers for about 30 minutes....still nothing and wouldn't start.
Idiots forgot the tighten the wires when they put the new battery in. The cables were attached in a separate area under another panel from where the terminals are to jump the battery so I never saw them until the next day. Froze my ass off that night trying to get that thing started. Stopped by to tell the manager at Sam's, not as an FU to the guy that did it, just as a heads up. His response was..."well i talked to him and he said he tightened them, so.... "
So they must have magically become less than hand tight all by themselves?...in one day?... I think i was more upset at the manager than the idiot in the shop.
TL;DR version - Check your cables.