Took me 6 hours to figure out a Mewp wouldn't start because of a loose battery terminal in 20 degree weather
Sat on hold with the rental company for an hour and a half before a guy named Dave asked if I'd checked the terminals, and I felt like a complete idiot because I'd already pulled the whole fuse panel apart looking for a short.
Heard a mechanic say once that 90 percent of no-start calls in winter are just bad connections, not dead batteries. Makes you feel dumb after tearing everything apart but at least Dave got you there.