Batt, Alt, or Slow Drain?
 

I'm currently having some electrical issues with my car at the moment. Whenever I let the car sit the batteries voltage drops down to ~10v, i'm thinking it's just not holding a charge like it should. Here's the symptoms though so I can just make sure I'm thinking correctly.

Car runs fine, and while running usually has upwards of 13-14v (by the stock gauge), I believe that tells me that my alternator is functioning at least partially at any RPM greater than 1k (I have Need-A-T2's dual headlights installed and whenever I have them up I get a major power drain. Usually drops my power down towards 12v while I'm at a stop light). I do plan on switching over to HID's in the future (year or two down the road... looking at engine and body first).

However after I drive and let it sit for a few hours (overnight, or while I work) the battery manages to drop down to ~10v which makes it nearly impossible to turn over. I've been lucky sometimes when I can just keep attempting to turn the car over and it'll eventually turn, but lately I haven't been so lucky.

Do you think it's a bad battery or a bad charging system?

Are you running a stock alternator?

Check the voltage at the battery with a DMM when its running. Stock gauge isn't all that reliable.

If you're getting a major drain with the headlights on, I'd start poking around there for something thats shorting out, or some wiring with high resistance. I've seen some headlight harnesses (from the stock three prong plug back) that are pretty green/black inside.

Yup, stock 70amp. I want to upgrade to high output, but I keep putting it off because I don't want to dig into the harness quite yet.
Alright. I'll see if my bro-in-law has one laying around. I would use mine but it's about 200+ miles away right now.
They're not stock plugs and I don't think it's a corrosion problem. I just think using halogen is actually eating up more amperage than stock hence why switching over to HID would remedy that problem--I'll look into the harness though. May even pick up some dielectric grease to squirt in the plugs.