So I've owned this car for a while now, and it started draining the battery whenever it's shut off. I know it could be the alternator but it'll start up just fine. The starter turns just fine and I can't figure out what the problem is. I did an OBDII on start up and it says everything is good. The battery just drains and I can't figure it out. A friend of mine said it might be the diode on the alternator but I'm not so sure. I checked the fuses and everything is good. This problem just came out of nowhere and now I can't seem to find the problem. Any help would be appreciated.