Wife's 2018 Mercedes GLA250. Car is 3 Years and 4 months old. Just turned over 12k miles. The AGM battery is at 12.25Volts after sitting unused for a week. Everything I read says an AGM battery should have a residual voltage of 12.8v ~ 13.2v. Car fires up and runs just fine with an initial charging voltage of 15.2v which drops back to around 14.2v after twenty minutes of driving. A lead acid battery is only 50% charged at 12.25v but there is a bunch of contradictory numbers out there when you search for similar info on AGM. Would really welcome some comments from folks who can forget everything they know about lead acid batteries before answering.
One other thing. The car lives in high ambient temperatures (Palm Desert, CA) Thanks much. Kiwipop