I thought my battery was just dead, when my car wouldn't start last night because the battery had no charge. However, it started fine this morning, and the battery was in the normal range.

Turn the headlights on, and it took a nose dive into the yellow zone....Any guesses on what it could be?

 

Sounds like your battery is weak. Sometimes when it sits after a load has been on it, it can seem to gain a little reserve voltage back. You also might want to check to be sure your alternator is putting out good voltage.

It could also be that you have a poor connection to the battery.

 

As soon as I turn the headlights off tho, it goes right back up...

 

I've seen batteries do that, show on a guage normal operating voltage, then when placed under a load they go way down. Does the car start? I'm with shoebox though I think your battery is dieing. How old is it?

 

Car starts fine, and runs fine, until the lights go on, then the battery loses voltage. No idea on the age of the battery, I just bought the car.

I think it may be a bad connection on the alternator...I saw some blue-green looking stuff under the little rubber cap where the pos. cable plugs into it...I'd try it now, but it's getting dark.