High volts


Where you said that several batteries have been installed, I don’t think you have a battery problem which will cause over charging.

Most often voltage drop in ignition and regulation circuits cause over charge problems. If voltage regulator is seeing low voltage in harness it will boost voltage output of alternator by the difference from normal harness voltage. In other words if VR is reading 12.5 volts, and battery is at 14v, alternator will add +1.5 volt to 13.5, and charge at 15 volts which will boil a battery dry, and kill it.

You need to check for voltage drop in ground side of ignition circuits, and plus side as well. Ground side should show no voltage drop, and plus side no more than a total of 0.3 v.

Corrosion at any connection, bad conductors, loose connections, and worn ignition switch adds resistance to circuit which causes drop in voltage. There will be a small voltage drop at each of the above that all add together to make one large resistance. You need to sniff out, and eliminate as much of this age related resistance as possible by cleaning, tightening, and replacing conductors as needed.