Volt Meter not working

[aboatman]

I have a 90HP Outboard motor, 2 stroke. My volt meter started fluctuating from 13v down, then to 8 to 0, the needle bounced arround and now it's completely inactive. I have 1 new battery, 1 battery 12 months old. I have a vhf radio and running lights (17 ft vessel). The boat starts fine even with the volt meter no-op. Is this the guage, charging system from the engine or are the batteries weak? Thanks

[99yam40]

Hook up a hand held meter to the system and see what is working or not working and you can have the batteries tested at a auto part store