Alternator Overcharge

On the back of the engine there is a plug at the firewall, pull it apart and check for corrosion. If it's corroded, clean it and that should solve your problem. Also check your battery for a bad cell, this can cause the regulator to see a low battery condition.

It also could be your regulator but check the other two things first before you start replacing parts. I've watched "mechanics" replace everything in a case like yours and still have the same problem, you can spend a couple hundred $ and find out it may have cost you some time only.

Let me know what you find.