I shall try again.
My boat's gauge and my garmin 220 fishfinder both read 14.8. Is this too
high and should I be concerned?

When does it read 14.8?

When the alternator is running?

Your voltmeter will read at a higher number
than the battery's state of charge when there is current from the alternator
present.
You won't get a reading that reflects only the battery voltage until you have
discoed the charger or alternator current.