Where is the battery on the 2004 touareg?

Under the drivers seat. OK, let's add to this...

It's a tad more complicated. There are two plastic covers at the front of the seat on the floor. You need to lift both of them up. That exposes a fastener that will require a 10mm "triple square" male tool. This is similar to the familiar Torx (6 point star) fastener except it has 12 points instead of 6 points. This tool is available at many auto supply places, without it, you will NOT replace the battery. Remove both screws (they're TIGHT!!!), remove the plastic trim pieces from the rear of the seat slide assembly (carefully snap off) Tilt the seat back all the way forward, slide the seat forward almost all the way but leave space to miss the steering wheel. Now push back on the seat back and the entire seat will tilt to the rear exposing the battery box under the drivers seat. There are four clips that hold the cover on, unhook them, remove the torx screw holding the heater deflector to the battery box lid, remove the wire tie holding the wire to the top of the box and remove the box cover. Now you see the battery. Remove the gas vent plastic pipe from the front, remove the metal cover at the front left corner (10mm socket) it will not come out until you remove the (-) cable but don't just yet. remove the side clamp (10mm socket) and the battery is loose and free. It would be smart (but not required) to provide a 12 volt electrical source to the battery terminals as you replace the battery to help keep all of the radio GPS etc, settings. Remove the terminals, lift out the battery. Now reinstall it all the opposite of how you removed it. I believe VW hired a team of engineers for a year to design the HARDEST battery replacement system that anyone could devise!!! Dave