12V battery - expected voltage?

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Jul 23, 2019
What is the expected voltage reading for the 12 V battery? VARTA ...
Ours seems to be jumping around quite a bit 12.24 to 12.30 or so
Charger is plugged into car, but scheduled to not start until early morning.
Car is 22 months in service, only about 5000 miles.
One reason for concern is wife had car out, would not start up, EPC light on dash. Then after a while it worked.

Next day – car had charged overnight, we let it rest then rechecked the voltage –
Initially, having opened the door to get to hood release, we saw 12.23 and heard a (fan?) motor run sound.
Then after a while that sound stopped, and the voltage started climbing - reached 12.70
Now, 6 hours later, we see 12.65 (car undisturbed in the interval)
So apparently opening the door starts some current drain, dropping the voltage temporarily.
Seems the battery is probably OK.
Wonder if the 12V charging apparatus is intermittent ...

Still unexplained is the EPC indicator and failure to start operations.
My guess is the same as an ICE car. I have not closely monitored the 12 V battery, so don't have data. I believe the 12 V won't charge unless the car is charging or turned on. The easy fix is to get a new 12 V battery. I have almost 27,000 miles on my car (3 years old) and still using the original 12 V battery. Since the motor bay does not get very hot, and since I live in a pretty mild climate, I'm hoping to get 6 to 8 years out of the 12 V battery, as that how long the 12 V battery typically lasts in my 2001 Volvo V70 (12 V battery is at the rear of car where it stays very cool).