The alternator supplies the vehicle needs, running down the road, unless the load is greater than the alternator can handle, then it will take some out of the battery. There should be an indicator lite or something on the dash to let you know of a discharge situation, that is when to do the testing. Get you a cheap dmm and carry it with you. When you see the discharge situation, pull over, check the reading at the battery posts. With the engine running I like to see the reading in the high 13s.
Saturday, March 7th, 2009 AT 12:26 PM