The battery was dead on my '99 Blazer this morning so I jumped it but as soon as the jumpers were disconnected it died. So I put another battery in it and it started but the alternator is only charging at the first large line to the right of the the 9(bottom). I guess that would be 12V? When revved up it gets to 14. My headlights are on all the time if that means anything. So is my alternator shot or is this normal? The battery that was in the car was fairly new and the cables and connections are good. I found no reason for the battery to be dead(lights on, etc.). ???? So since I posted this I've determined that my alternator is bad. I called to see about a replacement and it seems there are several types, that is amps. How can I tell what amp it is? Well nevermind on this post, I already found out all I need to know.

 

you need to check with a real volt meter. Gauges aren't that accurate. Engine running it should be over 13v.if so alt is good.

 

You can get a DVOM at Harbor Freight Tools for 4.99. Set the DC range at '20 VDC' and you should read 13.7 VDC +- 0.1.

 

are you running anything that isn't stock? Amps, efans, extra lights or anything like that?