2005 gx. It sat for about 3 weeks. Went to start and the battery was dead. I jumped it drove it home. I removed the battery had it tested and it was fine. I charged the battery with my battery charger. I drove it for a week. I went on vacation for two weeks and I tried to start it. It started fine. Out of curiosity I threw the charger on it again and the battery was at 30%. Would this be a bad alternator? My buddy had an Avalon and he said it had the same symptoms. He had the alternator tested and it was fine. But he replaced it anyways and it fixed the issue. I’m hoping it’s the alternator and not a bad ground somewhere. There is not an aftermarket stereo in it so I doubt it’s a bad ground.
probably not the alternator. There is parasite draw someplace. Not common on pre-computer cars, and easily diagnosed on those. Newer cars are always "on". There is always some computer memory being used, usually not enough to draw a battery down over a few days. But as connections get older, and batteries get weaker, it becomes enough to draw the battery down.
So your car is getting older, less efficient electrically, the battery doesn't have the depth it once had. All combined means it won't last as long without being driven enough to recharge the battery.
Certainly its possible your alternator isn't putting out enough, but doubtful. Probably a new battery would do you more benefit. But I certainly would test the alternator to be sure.
If your driving it every day, your battery is probably just fine.....for a long while.
We have that issue with Mother-in-laws car all the time. everything is working as it should, Battery is about 9 month old, etc. But over time, if not driven far enough to recharge the battery, it will go dead. My Suzuki DRZ400 is the worst. Battery won't last a week. So it stays on a tender all the time. My other bike isn't as bad, it will go dead after about 2 weeks.