I had my battery naturally die 2 days ago. Truely a unique experience. It was not lights left on or anything, just an old battery that finally died.

The car was running fine all the way to the store. Went in and got some chicken, came out and turned the key and nothing came on. not a lick. Thought something came unplugged. Then I tried it about 3 more times, and the whole car went nutso... opening windows and the sunroof (slowly) the warning lights blicking on and off, I felt like I had a AA battery running the whole car.

After I changed out the battery I realized it has been going for a long time. Everything is so much brighter and my car starts up crisp again. It is weird.

And as an interesting side, my radio still worked after I changed batteries. So I am wondering if anyone else has had the radio work after power loss. My guess is that the Audi dealer jimmy rigged my radio. My clock shows the battery was cold for 15 minutes. The only thing I can figure is there is a capacitor for the the presets and it kept the radio alive or someone decided the safety feature was annoying.

 

Sounds like your battery might have lost a cell suddenly. Have found that batteries die one of two ways; they fade away, usually in cold weather or they die suddenly. The sudden death ones are often caused by a cell no longer making contact. If you test the battery, u get 10 volts instead of 12. each cell is 2 volts. Sometimes they make intermittent contect and can work for a while.

If your battery is fading away, easiest way to check is my using the lights. If they dim when the car is at an idle, and get brighter when you step on the gas, you generally have a weak battery. The reason for the light brightness change is due to car using the alternator to provide power, and it produces more amps at higher RPMs.

Not sure about the radio, it is possible that it got some power to keep it active, or they have a safely capacitor to prevent it from locking if power is lost. Don't these radios do some sort of funky lock mechanism where they talk to the main computer and are paired to only work with the car's main computer so that even if they loose power, they still work? I though I read that somewhere, but it could be a different car too.

 

Actually my battery did a very similar thing. Just one day out of the blue it decided that it would not start my car anymore. I charged it for a couple hours and it did manage to start but once turned off it would not start again.

I took the car to Autozone and they checked it. They told me that the battery is dead because the alternator was good. Bought a new battery and the car has never ran better. A week later a buddy of mine's car started not starting up after sitting for an hour or so. He had just recently bought the car and it was an 01 VW Passat ... my car is an 01 Audi A6 ... same battery ... same basic mechanics. His battery was also dead ... seems that battery life span is generally fixed and it seems like 4 years is the span for the OEM battery. At least for us it was.

Odd, huh?