nickfrost

I have a 10 year old RS-4. Absolutely standard and unmodified.

Suddenly, the battery drains flat overnight. A quick investigation with an ammeter shows that the radio (inc Bose, satnav, CD changer, etc.) is drawing about 3A, all the time. Removing the radio fuse "cures" the problem.

But what is the probable cause? Which of the many components might need fixing / replacing? Apart from the battery drain, it all seems to work correctly.

NormS

I have exactly the same issue on my '07 Q7. I replaced the original battery (9 years old!) but the new battery went dead in 2 days. Old battery still checks good! I read here that computer must be reprogrammed after battery change but Audi dealer said no. I got suspicious about the drain on the battery and I found the same issue. When removing the Bose DSP 30 amp fuse, the problem went away and the battery and all components work well. When the fuse is in, the radio works fine but the battery goes dead overnight.

nickfrost

Thanks NormS for confirmation that I am not alone! But where do we go from here? (Interesting that yours was also about 9 years old.)

NormS

I suspect there's a bad component on the amplifier circuit board that turns it on/off with the ignition switch. The subject fuse supplies full time 12v power from the battery. Likely, the dealer fix is to replace the amplifier and I'd guess you could buy a nice used car for what they would charge. My thinking is somehow change the power source to this amp circuit so it shuts off with the ignition switch. I am checking to see if the fuse block where this 30 amp fuse is located (rear compartment by the tail lights on the Q7) has a switched accessory power buss as well as the battery 12v buss. Due to amperage, it may be necessary to insert a relay to keep the amp power coming from the battery so only the relay coil connects to the ignition buss.

nickfrost

Yes, that was also my thought - add a relay to actuate the radio system only when the ignition is on. Not a big deal, but it's annoying to have to do it. As you say, it's one duff component, somewhere - but which, and where...?