alternator battery

I would make sure the belt's tight first, then I have this cigarette lighter 
plug in deal I bought for a few bucks.  You put it in and do stuff like leave 
the lights on with the car off etc.  and a pattern in these three leds matches 
the chart and tells you the problem.  This might be available at an auto parts 
store and it seems to have worked for me in the past.

Mark M.