Good evening,

I have an Audi Q7 from 2007. I recently changed the battery thinking that it was old (I bought the car in October 2025) as it was flat overnight.

After about 2 weeks with the new battery, the same issue started, battery was flat (10%) in the morning.

Now, it was Easter weekend so I didn't use the car but tonight I wanted to check the jumpstart kit (if it's charged properly) so that tomorrow morning I can use it:

car won't open.

But even worse, when I use the manual key (I have 3 + a plastic one) no way to turn the key in the slot, it's not opening the car.

Actually, funny enough, the same issue I had with my A3 but luckily it opened the boot, which is not the case now with the Q7.

Any ideas about how to open the car ? And why it's draining the battery like this.

Ah and tonight, lights were on on the dashboard...which is also weird.

Thank you in advance for any ideas.

V.

Edited April 6Apr 6 by Vanessa123

Bon soir/Guten Abend Vanessa.

I don't know how to open the car; perhaps others can advise.

There are many possible causes for the flat battery so can we start by getting some more information. Was the new battery coded to the car? Have you had any diagnosis done by an electrician? Have you fitted extra electrical equipment such as a satnav, a dash camera, a phone charger, a new stereo system etc?

Good evening !

I don't know what you mean by coded but what happened is that I bought the car with a battery and after 5 months suddenly the battery was flat in the morning (but just enough to open the car with the fob) so my guess was : old battery / must change which I did.

New battery was installed, but to be honest I don't know if it was coded.

Anyway, at the beginning it was OK but after 2 weeks, same scenario. Battery flat in the morning.

One day, I parked the car at 12.30 noon. I checked the battery at 6.30 pm: 100%

again I checked at 8.30 pm, 100%

but then I went at 1.30 am in the night and it was down to 10%. But I still managed to start the car !

Next morning, 10% but can't start the car.

This is weird isn't it ?

Thank you for the reply.

Now the car was taken away to the garage and I hope he will manage to open it. I was told that under the car you can pull some cable that opens the hood. Let's see.

KRS, Vanessa

ps: the Audi is from 2008 not 2007

Edited April 7Apr 7 by Vanessa123

Coding the battery means to programme the charging system for the type and capacity of the new battery to ensure it is charged at the correct rate. It is done with a computer gadget plugged into the car, and is not something the average owner would do himself. It's the sort of job best left to a professional because of the equipment cost. Unless the coding is done it is possible for the new battery to be damaged.

I am curious to know how you are measuring the battery strength as a percentage. The meters I am familiar with give readings in volts not percent.

You have not mentioned the extra electrical equipment I asked about, nor any diagnostic work.

Hello,

Thank you for your answer.

So I got my car back yesterday. They managed to open the car, they charged the battery and coded it indeed (apparently the other garage had only changed it but not coded)

So they kept the car a couple of days and had no issues, it did not get flat.

So the only difference with the garage and my place is that I live up the hills and that the car is parked in a slope. He asked if I was putting the handbrake on, I said no because it's automatic. But he said I must because the ABS of the car stays alert etc...

So i did put the handbrake on, next morning OK still 100%, but in the afternoon today I checked, 10%.

So how to I measure ? It's in the car, I press the "car" button and select battery level, there I see how much battery I have.

Now I moved my car to a flatter place. I'm really mystified here.

As for the extra electrical equipment, I have not fitted anything new myself, but there is carplay (which is deficient at the moment: I can see display but hear no sound)

I didn't do any diagnostic work on it and the garage didn't (he is audi specialist) because he said: we can't see this on computer diagnostic...

Thanks again

Edited April 11Apr 11 by Vanessa123

I'm glad to read you can enter the car again. Let us hope the battery has not been damaged by the time it was uncoded.

Assuming the battery level shown in the car is accurate it seems that there is something draining the battery. The obvious suspect is the defective car play device, however it would be worth visiting an auto electrician to get confirmation of that before spending any more money. He may find a fault in the alternator for example which can also drain the battery. (It is unfortunate that even specialists sometimes rely too much on the computer, and too little on their brains, when a diagnosis is needed.)

In the meantime it would be worth connecting a battery charger overnight if possible, to keep the battery charged.

Hello again,

Thank you Cliff !

So the garage said he checked the alternator but he said there was no issue.

Now It is the 3rd time the battery reaches 10% and I can actually start the car.

This morning the battery was at 10% at 7.30am. I turned on the car (which is weird that it worked) then later charged it by driving a bit and letting the engine on.

So at 9.30am it was fully charged.

At 8.30pm, I check it: 100%

At 11.30pm : 100%

But at 1.30am : 10 % and I can start it.

I am wondering, something is happening and it drops all of a sudden. Anyone can explain to me how this is possible ?? Even phones don't do that !

I left the hood open now and the doors. I can jumpstart it in the morning.

If only someone else had this experience before to explain :(

Good night, and thank you for your advices.

ps: I thought it is better not to charge the battery with a charger when the battery is connected to the car ...

Also, how can the carplay be responsible for the sudden battery drain ?

Vanessa.

[1] I have no idea how Carplay can drain the battery. I don't even know what a Carplay looks like, but you said it was defective so it seems a likely cause of the problem.

[2] I am still suspicious of the battery indicator in your car. To accurately measure battery condition is not an easy task, and the fact that you only get readings of either 10% or 100%, with nothing in between, makes me even more suspicious.

[3] It is perfectly possible to charge the battery while it is connected if you use the correct type of charger. The bulky old fashioned high current chargers that output as much as 10 amps would be unwise; a modern so-called intelligent charger that monitors charge level is fine.

As i said before, I think you need the help of an auto electrician who can properly test the flow of electricity in to and out of the battery, not a car technician who can only read error codes from a computer.

Hello,

I have some news !

A neighbour, former mechanic and mechanical engineer tested the amount of battery drain, it was 1 Amp .

So what we did is remove fuses one by one to see which ones could be responsible.

We found 2: the navigation system and the digital sound package control unit , each of them drawing 500mA

So after removing the fuses after I parked at home, next morning the battery was at 100 %

When I drive I put the fuses back in (to be able to check battery level and suspension and have some radio )

My partner is also a mechanic and he is coming back next week from abroad, he will have a look at the defective equipment.

Voilà, thank you again for the advices !

On 4/13/2026 at 11:08 AM, cliffcoggin said:

Vanessa.

[1] I have no idea how Carplay can drain the battery. I don't even know what a Carplay looks like, but you said it was defective so it seems a likely cause of the problem.

[2] I am still suspicious of the battery indicator in your car. To accurately measure battery condition is not an easy task, and the fact that you only get readings of either 10% or 100%, with nothing in between, makes me even more suspicious.

[3] It is perfectly possible to charge the battery while it is connected if you use the correct type of charger. The bulky old fashioned high current chargers that output as much as 10 amps would be unwise; a modern so-called intelligent charger that monitors charge level is fine.

As i said before, I think you need the help of an auto electrician who can properly test the flow of electricity in to and out of the battery, not a car technician who can only read error codes from a computer.

Dear Cliff,

The carplay is the function to connect your phone to the car and to reflect the phone's screen on the display.

The battery indicator did not only indicate 10 or 100 % but sometimes 40% or 60%

:)

So as I suggested on April 7th the satnav and the stereo have been wired into a non-switched power supply. Change those to a fuse controlled by the ignition switch to permanently solve the problem.

Hii Cliff, Thank you ! I will take note but could the problem be due to a leak and corrosion ? There was a lot of rain here recently, maybe dampness ? or leak through the panoramic roof ?

I know on an earlier post that a member had battery drain via after-market stereo.

Back to post. Only way to accurately measure battery is with a cheap multimeter. Don’t use on board MMI connection.

You’ll know if car is damp. Drain holes for panoramic are under front door hinges, and at rear, under wheel arch liner. Panoramic can leak, either at cassette drain points (one each corner of sunroof) or the actually cassette itself. Check carpets for any dampness.

The battery drain check by your neighbour is 100% right approach. Unfortunately there’s no quick fix, it’s laborious, but it needs to to be systematic and go through all scenarios. Also check the car is not dropping on suspension overnight.

11 hours ago, Vanessa123 said:

Hii Cliff, Thank you ! I will take note but could the problem be due to a leak and corrosion ? There was a lot of rain here recently, maybe dampness ? or leak through the panoramic roof ?

It is not likely; neither is it impossible, but we shall not solve the puzzle by guesswork or by intuition or by witchcraft. It needs somebody with a meter (not the car's display) and some electrical knowledge to test each circuit, as your neighbour started to do.

Thank you very much for all the advices !

I know it's an after market head unit and the guy that installed it was not very good (we discovered other botched things).

My partner will have a look at it and then we will see what to do. Thank you so much !