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I have not been driving the S4 for a couple of months since I bought another car.
I have kept the battery trickle charged but I have found the keys don't work on the remote. I have to put the key in the door to open.
I was going to change the batteries in the keys but when I took the key apart noticed there is no battery.
Does the key charge up when driving? And how long would it normally take?
Can I stick it in the mains socket to charge it?



















That last one was a joke.

I think when the battery's disconnected the car doesn't recognise the fob.

There's two possible ways to reprogramme it:

1. Key in the lock, unlock the door with key and then press unlock button; then lock the car with key and press lock button.

If that doesn't work you need both keys:

2. Put one in and turn on the ignition; on the other press the lock and unlock buttons separately. That should do it.

Had the same problem and the second process worked for me.

I think the fobs have a passive RFID tag in them that doesn't need a battery.

Nice one Biyitch, i'll give that a go.

What Biyitch says is all correct, I've done 2 before when I've disconnected the battery, or changed the battery in the key fob.

I'm sure there is a battery in the remote keys (i.e. the ones with buttons on to open the doors). The immobiliser part within the key may not need a battery to work, but the remote central locking buttons definitely need battery power, so I'm not sure how your key could work without one.

I went to the car last night and my key remote worked again. I had not got around to trying the fix yet. I have had the key in the ignition for about 15 min over the weekend and it still make me wonder if they do charge up. I have heard of this before but I wasn't sure if Audi's do it or not. The battery has not gone flat on the car as I have it on trickle charge.

When I originally took the fob apart to change the battery (thinking it was a flat fob battery) there was what looked like a battery pack unit rather than any battery. It looks like a sealed unit.