Battery gauge question

[85blzrboy]

My 1985 k5 battery gauge rises into the red zone when I take the expressway so thats above 55 mph. Then it goes back down to normal operating range at stops and most city driving. I just installed a new correct battery as the previous owner did not have adequate cranking amps. Any possible causes? There are no other indicators that I am aware of.

 

[smurph20]

Have the altenator checked and make sure its not over charging. Should be from 13.5-14.5 anything over that could damage the battery and more.

 

[89Suburban]

Voltage regulator in the alternator would be my guess.

 

[crazy4offroad]

Voltage regulator going out, and they are built into the alternator. Easy fix replacing the alternator, 2 bolts and a wire plug.