[vex]

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?