Jump start it, put the volt meter on the battery and rev the motor. Even if your battery dropped a cell you should see a jump in voltage when you rev the motor. If not, your alt took a dump or you have a loose/broken wire.
Nice thing is either part can be double checked at a FLAPS to be sure. Good luck, hope it's just a loose wire.

1956 GMC 370 dump " 'Tater "
1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI

I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P