Voltmeter/Alarm hoohickys

Are there any good voltmeter/alarms things that would work with a sailboat? It might help avoid getting embarrassed when your Rx battery cuts oout suddenly.

Is a volmeter (lightbar or gauge) better or an audible alarm? I’ve seen some circuits with an L.E.D. that sticks out of the deck with and beeps when the battery gets low.

thx