A full 12volt battery with no load on it and no charger will read about 12.6 -12.7 max. It's time to charge it at 12.1-12.2 voltz, which is 50% discharged. A dead battery is about 11.6. Any reading higher than 12.7 is from a charger or solar. If you shut a charger off, it will take an hour or so to get an accurate read. Also, if there is a draw on the battery, it will read lower than it is.
Gary Kowal, San Diego, CA
2018 Winnebago Minnie Winnie 26A
2dr 2010 Jeep Wrangler toad