2000 Dakota Volt Gage is going to 18 volts HELP

My wifes Dak. It has started giving her a Check Gages lite in the cluster and the Volt Meter Pegs. I haven't been able to get a volt meter on the battery cause it comes and goes. Don't see any issues with any other gage. She said everything else seems normal. 4.7 V8 4 wheel drive auto trans. Any ideas?