if you get the new powervision, you can datalog and that is one of the fields captured. i was playing around, did a short (15 min) datalog and my voltage reading stayed at a constant 14.1
I don't think the meters in the fairing are precision calibrated instruments so there will be variances high or low of the actual voltage. Using a calibrated VOM at the battery will give a much better reading.
My VM usually shows ~13.2V, verified by a VOM, and around 14V at the battery--both with engine running, of course. No problems.