Originally Posted by alexwhittemore
13.8V is what's called the "float charge" voltage for lead acid batteries. I'm going to assume you had the charger plugged in when you got that reading?
Anyway, yes, that's fine. If you're driving, you may get in the 14V range (depends on the alternator's MO, it's not going to be constant voltage in a bimmer). Anything down to just under 12V is probably acceptable. Not sure what the threshold for a low battery warning is. A deep discharge will be somewhere around 10 or 11V
I went to the dealer with my car key & he checked it on the key reader & toke a print out & said the car battery voltage is 13.8v, even i was surprised hwo he can check it without checking the battery in front of him