You probably could have just taken the battery inside and let it warm up and then tried it. I’ve had to do that back in day when I actually had to work on my cars. Oh my misspent youth; those were the days. 
Oops As I understand it, the guys put a pan of charcoal briquettes under the engine. Warmed it up quite nicely :rolleyes:
Autozone does a free battery & alternator check. I may try that but today the car worked fine.