How high is it? Is the reading for the chassis or house batteries? Do you get the reading plugged in to shore power (converter/charger) or from the engine running? (alternator)
Most alternators have the voltage regulator built into the housing. On the converter/charger, charging rate is set by the control board in it.
Have you cleaned and checked all battery connections, including ground connections? A bad connection can fool the charging current to go higher, reading low voltage from the batteries.