Hello,
I recently bought used 05' MCS. Unfortunately, remote key which came with the car was dead. I had to open and close the car manually. I tried to reconnect the key using this topic: https://www.northamericanmotoring.co...ad.php?t=45067. Sadly, it didn't work for me.
When I called the dealer, I was quoted over 1000 PLN which is over 350$ for the new key. Yikes He also told me that it is IMPOSSIBLE to make it fully funtional.

Soo, if the faulty key had to be replaced anyway, I took a little saw (which had a really very narrow edge) and I started cutting CAREFULLY, to open the remote key (which consists of two parts glued together really strong). After 10 minutes of cutting (including my finger, ouch) I finally managed to open the key. Voila! It turned out, that the key is powered via Panasonic VL2020 rechargeable Lithium battery. I swapped the battery aaaand... it worked! I tried to reconnect the key once more using the same process as mentioned above and now it worked like a charm! In my case, the recheargable battery was dead. It looks like it can happen. All the other parts were OK, so I called my dealer and told him that I don't need the new key. I realized I saved over 350$. WOW.

Some of you was succeful with only reprogramming the key. Lucky you I had to cut through the key brutally, and replace the rechargeable battery. It is really a feasible task. Battery was 5$. If your key is useless anyway, you can try this solution as an ultimate one

 

Yep, batteries don't last forever. Especially ones that see extreme heat and cold.

Cool you got it fixed and saved so much!