Help with Low Battery Warning

[twosaabs]

Hi,

Anyone had the "Low Battery warning" and know how to fix it? If I have the stereo on with the engine off for more than a couple of mins, I get a warning on the MMI stating that system will shut off if the engine is not started. I've also started getting a yellow battery warning in the center display when the ignition is on (engine off) stating "low battery - will recharge when driving"

Seems to be getting worse as I've noticed now that interior lights turn off after a minute or so with the door open, "coming home lights" don't work and I need to turn stereo back on every time I start the car.

I've put the battery on a charger and while it initially shows <25%, it fully charges in < 1 hour (with a ~ 3A max charge rate) so the battery doesn't seem to be too low. Still get the same warnings after charging it though.

The dealer has checked it a couple of times (don't know exactly what they did) and said everything is fine. My suspicion is a weak battery, weak charge from alternator, "phantom" power drain when off etc. To be far, car always starts fine and turns over quickly, so maybe it is more of a monitor error - car thinks battery is low when in fact it is fine...?

Any suggestions of what else to check / what to ask the dealer to look at would be appreciated....

Thanks!

2011 S4 6MT

[100Daily]

Read your owners manual. Everything you are curious about is answered in detail under the "Energy Management" section.

[Tyrnnus]

This sounds like a case of the gremlins...

You know the car is not fine because this continues to happen. I know this will sound like a pain but here goes:
I would go to the dealer and ask to speak with the service manager, take him out to your car and demonstrate the problem to him. He will either say "thats normal" or "hmm maybe we need to have another looks". If he says it normal ask to sit in a new car on the showroom floor and repeat what you did in your car.
It sounds to me like your alternator is not getting a charge to the battery. Could be a bad alternator, a short somewhere, or even a loose connection.

No matter what your car is under warrantee and should be fixed. You could also try taking it to another dealer, if possible, and explain the situation

[shonseb]

^^^ good advise, ask him also to do it preowned also. It's definitely abnormal.

[SwankPeRFection]

There is a very easy test to figure out if your battery is "weak". Hook up a voltage meter to the battery and watch it while you start the car. If the voltage drops significantly, your battery is bad and needs replacing. Anything under 10volts during startup is bad in my opinion. Also, with accessories running and the engine turned off, your battery voltage should stay pretty steady at 12 volts. If it's trickling off, it's bad. With the engine running, if you're registering ~15volts or slightly less, then your alternator is charging fine.

Remember, just because a battery can show voltage and recharge doesn't mean the cells inside aren't shot. A health battery can have load on it and maintain a steady voltage, a bad one will not. This is what you're testing for because you already know the battery is losing voltage just sitting there doing nothing with the car turned off only powering up limited systems. If it can't even do that, it's not a charging/alternator issue, 90% of the time, it's a battery issue (i.e. it's going bad).

[twosaabs]

Thanks for the suggestions / comments. Yes, I've read the relevant section in the manual and the car is behaving exactly as it should with a low battery. My question was more related to what has caused the low battery, since initial checks by the dealer didn;t turn up any problems.

My car is about 2.5 yrs old, has a 30 min highway drive each day and weather has been warm recently - so none of the conditions I would expect to see a low battery in.

The voltages seem pretty good - close to 12V when starting, 12.3 to 12.4V when off and accessories running and 14.5 - 14.8V with engine on or when charging.

Thinking back, I first saw the problem after a 2 wk winter vacation when the car wasn't used, then started in low temps. It's almost as if the low battery / power management system was triggered then and hasn't learnt that the battery has indeed charged up.

I'll keep a note of any sympoms etc over the next couple of weeks with the hope that the dealer will have a better look during the next service which will soon be due.

In the meantime, I was really curious if anyone else had observed this behaviour, and if so, how it was fixed.

[SwankPeRFection]

^^^ Well, then you have one of two things going on.

1) Truly a bad battery.
2) Something else causing a drain on the battery more than what it should be stock after you turn it off.

Do you have anything in the car electronics wise that's not stock? Stereo, alarm, dash cam, anything...?... think hard, even insignificant stuff can matter.

[twosaabs]

^^^ Well, then you have one of two things going on.

1) Truly a bad battery.
2) Something else causing a drain on the battery more than what it should be stock after you turn it off.

Do you have anything in the car electronics wise that's not stock? Stereo, alarm, dash cam, anything...?... think hard, even insignificant stuff can matter.

Hmmn ... good point. The absolutely only non-stock thing on my car is a USB hard drive for music connected to the MMI (with the Audi to USB cable in the glove box).

I would have thought that this would be powered off when the car is off, but easy to test. I'll disconnect the drive and see what happens over the next few days.... Thanks!