2000 Dakota Volt Gage is going to 18 volts HELP

I don't really know much about that stuff, but some stuff to ponder

First disconnect either alternator field wire and see if the problem goes away

The newer Mopars (don't know about yours) has the regulator built into the computer. Just like the old separate regulator, a poor ground at the computer or poor connection to the power going into it will cause the regulator to "think" the battery is low and ramp up charge voltage.

Either situation, poor ground or poor power could certainly "come and go." Intermittents are always difficult. The thing is, hi voltage may very well damage stuff including the computer itself, so I would not screw with this. Get it fixed, even if you have to pay. Someone more familiar with these might be privy to service bulletins that address typical problems.

Harness connectors, "wiggle test."