OK, so my battery checks out as good, and charges fine when the car is started. But it will not hold a charge over night. I haven't changed anything electrical in my car except the alternator recently. And it charges fine as soon as it is jumped, so could I have misconnected something so that the battery would discharge when the car is off? I have a multimeter, but I'm not sure what I need to check to figure out what is taking power from the battery. Help please.

 

could be a number of things but start with the obvious... Interior light switch on? Radio, is it hardwired in? Bad ground maybe??? How old is the battery?

 

AAAAAARRRRRRRGGGGGGGGHHHHHHHHH!!!
I wish the dang search was working.
The alternator may be defective.
With the ignition off you need to measure the amount of current draw, to start with. then you'll need to start eliminating things one at a time until the current draw drops to normal (about 2-500 milliamps).
Have Fun!
hehehhe

 

The interior lights are not on. I have changed NOTHING except the alternator. Also, the battery is new. So, a defective alternator would cause battery discharge overnight?

 

Internal short could easily do it.
Also squirrels like wires

 

maybe that is what is wrong with your injectors

 

a Noid light will tell me that.