It's not likely the alt. isn't turning fast enough. If you have a lot of acess. like electric fan & A/C it could be too much load for the alt. Make sure the belt is good & tight. Even a new alt. can develope a shorted diode & it's output will be greatly reduced. Put a volt meter across the bat & check the charging voltage. It should be about 14 volts. Turn on some access. & rev it a little. It should go back up to 14 volts. This must be done with a well charged bat.
