Over charge with rpm input

Also, check to make sure your battery hasn't got a dead cell. Stop the engine and turn the high beam headlamps on for one full minute, then turn them off and put a voltmeter across the battery + and -. You should read something very close to 12.6 volts. If you read something closer to 10.5 volts, the battery's got a dead cell and the ammeter will peg every time you rev the engine up (though usually the ammeter will also dip to the left at idle).