so as it happens, the battery does read at 12.7 v.
but I was getting this intermittent display of parking brake actuator fault. Of course I suspected the battery.
A deeper look showed the fully charged battery with a capacity of 380 cold cranking amps. 1/2 of what it should be.
I only got 3.5 years out of that battery… I wonder if the noisy alternator had something to do with it. So I replaced that too.