Help diagnosing battery issue
 

My S4 vert is completely dead -- no door lights, no beeps when the key is in, nothing. If I jump it, it will start right up and run fine, and after turning it off I can crank it again right after, but after sitting for a while it's dead again.

I'm not sure if something is all of a sudden leaching power from the battery, if the battery is just done, or if maybe the alternator is the problem. I don't know much about auto electrics, but I do have a voltmeter so if you can offer suggestions about what to probe, I can check and narrow down the problem.

After a jump start, the voltmeter on the dash reads about 12.5, which seems a bit low to me. But again, I know nothing.

Thanks!

Take your alternator to Oreilly and have it tested.

If you dont know when the battery was last replaced, it probably needs to be replaced.

After the new battery see if its still dying overnight.

I had the same issue, I unhooked my battery and charged it and then I would touch the positive cable to the terminal on the battery and I would hear a click up around my headlights, so unhooked my headlight motors and the click was gone and I haven't had a drain on my battery since.

If your car has an old factory alarm in it, tear that crap out,

I had a similar issue with my Mazdaspeed Protege. I wish I could take back all the time and money I spent before I finally realized it was the 15 year old alarm finally taking a crap and killing my ignition.

Thanks for the suggestions! I'll start working on them and see where I get!

Good to hear, there's nothing more annoying than tracking down electrical bugs