sb730

Long time reader, first time poster.

I recently replaced the battery on my 09 A4 2.0T after several weeks of weak starts and the car slipping into conservation mode when off for more than a couple of hours (e.g. dome lights not turning on when opening door).

I replaced it with a new NAPA AGM battery. Install went fine. And car starts fine now. However, after leaving it off for a few hours and returning, seems like the car wants to slip back into conservation mode. When I unlock the car, dome lights turn on for a second, then turn right back off, and don't turn on when I open the door.

I've driven at least 60-70 miles since installing the battery. From what I've read, I don't think I need to reprogram the BEM since it's an 09 and it should "learn" about the new battery on its own, but correct me if I'm wrong. I've ran a multimeter through the cigarette lighter - runnning ~12.5V the entire time while driving at various RPM's.

Any insights as to what's going on?

uberwgn

SB, Welcome aboard!

If you have access to the VCDS program, you should tell the BEM that there's a new battery in there. Problem is, when you replace a very weak or dead battery, it can take quite a period of time (weeks? months?) for the car to learn that the battery has been replaced.

Others have experienced this. The car and the electrical system are doing their job and offering this protection enabling you to start the car. The car will figure it out sooner or later and give you full power to all systems ...

sb730

Thanks for the insight. I actually don't have VCDS. Is there a good place to get it from (Ross-tech is what i found when searching - is that a good place? How much should it cost?).

Also, if I don't let BEM know about the new battery, can it potentially damage the new one? I can live with the dome lights, etc., for a while if that's the only impact.

Thanks, and pardon the newbie questions.

uberwgn

Ross Tech is the only source I'm aware of for the cable unless you can find a used one. I think it's $400.

I do not believe the new battery will suffer any damage. I just can't answer the question about how long it might take to "adapt" itself. (It may be shutting down/cutting back on resources more than you realize. Supposedly it goes after HVAC first.)

snagitseven

If you want full function, support and ongoing firmware updates, get the original VCDS cable from Ross-Tech. While it's $349, it's a good investment that will more than pay for itself over time. You'll need the HEX-USB+CAN version and their free software download (PC only; will work with a Mac running PC emulator software).

http://store.ross-tech.com/shop/VCHUC.html

audi8k

12.5V while driving sounds too low.

sb730

Turns out the car apparently figured things out today - no longer operating in energy save mode. Hopefully that's done now. Thanks for the help!