'05 Malibu mystery battery drain

'05 Malibu (not a Classic) with about 150K miles used as a commuter car (90 mile round trip, 10 times or so a month). Typically, gets driven to work and back, then sits idle for a few days. AC Delco battery not more than a year or so old.
About a month ago started to occasionally find the battery weak, or dead when I would try to start it. A quick jump start and it would drive to work where it would sit for about 24 hours and then start right up for the drive home. Two days later it would start fine...or sometimes not. I verified that there is nothing on in the car. The dome lights go out, nothing plugged into the 12 volt outlets, etc. It seems that the alternator is good, since I can't imagine the battery lasting for a 1+ hour drive if the alternator wasn't working.
Recently determined another factor: The night before I go to work, I bring the car from the curb into the driveway to save a little time in the morning (and stumbling around in the morning darkness). The car probably runs for about 30 seconds or so. Even though the car has been sitting for a few days, it'll typically start right up for the short trip up the driveway, but then 9 hours later when I try to start it, the battery will be dead. Or sometimes not. Completely random.
Put a ammeter on it after one of these "dead battery" episodes and after the lights went out, etc, found that there was a 1/2 amp current draw. Verified that nothing was on in the car (keys not even in the ignition). I could not isolate where current draw was coming from. Any ideas?

'05 Malibu (not a Classic) with about 150K miles used as a commuter car (90 mile round trip, 10 times or so a month). Typically, gets driven to work and back, then sits idle for a few days. AC Delco battery not more than a year or so old.
About a month ago started to occasionally find the battery weak, or dead when I would try to start it. A quick jump start and it would drive to work where it would sit for about 24 hours and then start right up for the drive home. Two days later it would start fine...or sometimes not. I verified that there is nothing on in the car. The dome lights go out, nothing plugged into the 12 volt outlets, etc. It seems that the alternator is good, since I can't imagine the battery lasting for a 1+ hour drive if the alternator wasn't working.
Recently determined another factor: The night before I go to work, I bring the car from the curb into the driveway to save a little time in the morning (and stumbling around in the morning darkness). The car probably runs for about 30 seconds or so. Even though the car has been sitting for a few days, it'll typically start right up for the short trip up the driveway, but then 9 hours later when I try to start it, the battery will be dead. Or sometimes not. Completely random.
Put a ammeter on it after one of these "dead battery" episodes and after the lights went out, etc, found that there was a 1/2 amp current draw. Verified that nothing was on in the car (keys not even in the ignition). I could not isolate where current draw was coming from. Any ideas?
With your amp meter connected pull one fuse at a time. If the draw drops check out what is on this circuit. Sometimes your alternator can have an internal failure disconnect it and check if the draw drops off. Sometimes a relay can stick pull them one at a time. You will find the problem just take your time.

Yes, even though your alternator seems to be working, it might be not working good enough. With the car running, hook up a volt meter to the battery posts. Should read somewhere between 13 to 14.5 volts. If not, the alt is faulty. If it reads fine, then while it's running turn on all accesories like high beams, radio, A/C, etc and recheck voltage. It will drop some then steady, but should still be above 13 volts. It sounds like a charging issue rather than a draw.

How old is the battery? Has it been tested? Need to make sure it's in good shape. Also when checking for draws, after power has been restored, some modules can take up to 20 min or more to go to "sleep". Wait at least 20 min before pulling fuses to be sure what your are seeing is not a normal condition.

Good advice from the guys......

A 90 mile round trip, should be more than enough to charge a battery for a few days......

Does the car have a voltmeter in the cluster? What does it read while driving?

GMTech1 is correct about draws......when you disconnect a battery(neg cable) and immediately insert an ampmeter in series, modules could be alive.....some vehicles can take anywhere from 10 minutes to half an hour, for modules to stop communicating and go to sleep(if it has Onstar, it can intermittently run, just a few seconds, during a test).....