Here is a mystery that I am about to jump off the bridge about.
I have a 2001 Audi A4. I used to keep it in a garage and drive it about once every second week. It would start up every time, no problem.
After installing a new radio, and then being away for about a month, I came back to find the side blinker lights stolen (read: ripped out) and the battery dead. Assuming they were separate issues, I repaired the lights, bought a new battery, used my radio, and life was fine.
But after this, the car would not start if left more than 5 days without driving.
I took it to the dealership/mechanic, and explained the problem. They checked it, but couldn’t find anything wrong. They kept it over night on a sensor and said that the battery was not draining and everything was normal.
I took it home, and the problem continued. So I took it back and made them keep the car for a week, and over the weekend, and on Monday, of course, the car started just fine.
The problem persisted, I took it to a mechanic friend, who also couldn’t find anything wrong with it other than a cheap battery.
I bought the Audi recommended battery ($$$) and had a mechanic put it in a check everything and all was deemed in working order. They ruled out battery drainage, the radio, faulty wiring with the side lights, and the alarm.
I took it home. And now, it is touch and go. I can leave it 7 days it is fine, and then again (like this morning) it can sit for 5 days and be completely dead.
Please help before they find me running around the neighborhood in my underwear screaming nonsense about battery life!
You need to have someone look for dark drain. Modern cars use energy all the time. They keep the computers alive as well as the security system. There are usually lots of things using that battery when the car is parked.
Most of the things using energy use very little and most of them stop or reduce energy use after a period of time. Anti thief devices are first on the list, but the alternator and other parts may be the problem.
Since it takes some time for all these energy users to normally go down to sleep mode, it can’t be checked in five minutes.
It is also possible that somewhere along the line the alternator was damaged in a way that is not easy to check, or the new battery is not as good as you would like.
I would suggest one thing that might show up the problem. disconnect all power to that radio. See what happens.
Note: solar re chargers are available that might work for you, if you park outside or a battery tender (small low power battery charger designed not to over charge the battery).
Fixing the problem is not all that easy normally as it can be many different difficult to check items and with your specific situation, you have even more than usual.
Good Luck