What could be the reason why battery is not charging at idle speed? Battery light goes off when the RPM is above 1.5 to 2K and comes back on when it's under 1K. I have a cigarette lighter volt meter and it goes to 13V+ when driving and then it comes down to 11.5 to 12V during traffic or at a traffic light. I checked the belt and it seems on and belt tensioner is seems to be ok as well. Does this indicate that alternator is reaching it's end of life? My 98 has 169K miles.