12v battery question

So I took my volt to autozone, which they're clearly not very up to date lol but still. So literally right after shutting the vehicle off, they tested the 12v battery at the source and according to them it tested good but the charge was at 50% oddly. The AutoZone worker said it may be the alternator which it doesn't have one lmao. My question is though is that normal at all? All my research says that no that means the 12v is actively dying and I've seen people say that agm batteries for some odd reason tend to test good even when going bad. I can't find a date or anything on the battery anywhere. It appears it's oem since no date and it's ac Delco. It's 2017 LT. Also have a check engine light on that reads evap and low refrigerant? Seriously wondering if the 12v is causing sensors to malfunction because also my mode button doesn't work unless I reset the battery and then it only works for like a day or two. Also the other day my trunk sensor wouldn't go off until I reset the 12v.