Why is the dealer telling me it cost $500 to replace my battery and no one else but them could do it.

The cost to replace the transmission control module (TCM) on a 2003 Audi A4 can vary depending on several factors, such as the location of the repair shop, the extent of the damage to the TCM, and the cost of the replacement part.
On average, the cost of replacing the TCM for a 2003 Audi A4 can range from $500 to $1,500. This cost includes the cost of the replacement part and the labor involved in the repair. However, depending on the extent of the damage to the TCM or if other parts need to be replaced along with the TCM, the cost can go up significantly.
It's always a good idea to get a quote from a reputable repair shop before proceeding with any repairs. They can provide you with a more accurate estimate based on the specific details of your situation. Additionally, if your Audi A4 is still under warranty, the cost of the repair may be covered, so it's worth checking with your dealer to see if this is the case.

Probably - fully computerised cars, I hear from colleagues, often need dealer level diagnostic equipment to "tell" the brain it has had a replacement.

Envoys (and Trailblazer, Bravada, Ascender) between '03-'06, came from the factory with defective designed parts installed in the gauge cluster. Gauges can malfunction at most any time, most commonly with battery low voltage issues. Dealer cost may vary between $500-$700 depending on location. There may be someone in your local area who specializes in Gm gauge repair. Costs are usually reasonable. Research youtube for more info. Good luck.

Ron,
Speed-O-Repair.

You will need a good OBD2 scan tool.
try this you tube link

still need code notify dealer with vin or vehicle and proof of ownership ---99.9 % no charge for codes if they do code entry then may charge

charge battery then start it up sounds like alternator i used to own that car prob 500

Replace the battery in the keyless entry. Pry the plastic apart and look at the battery...should look like a watch battery or simply take it to a dealer and they should replace for the cost of the battery.
If this doesn't work it will need to be reprogrammed. You manual should tell you how.

At you mileage, I say its due, not worth risking it breaking and bending the valves, also recomended changing are the water pump, timing belt tensioner, and idler for teh regular belts
Probably cost around $500 - $750

you need to replace your altenator and battery