The battery that operates the remote lock/unlock in one of the keys for my '97 E420 has apparently died. Is this something that needs to be replaced by the dealer, or can I do it myself (and if so, how do I reach the battery)? Reading some other posts about the "handshake" system used in these keys makes me a bit nervous about doing my own R&R, but I hate to go to the dealer for anything if I can avoid it! Thanks for any help!

Instructions are in the owners manual.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

I do not believe that your '97 uses such a handshake system.

If your batteries are dead, you will likely have to synchronize the remote to the IRCL, which is a very easy procedure and is in the owner's manual. If that procedure fails, it means that your key is dead (or made for a different car, which isn't the case with yours).

Your key has a blade and you have a mechanical ignition cylinder. There may be a chip in your key which communicates with the computer to allow a start (or not), but that chip is not powered by the batteries in the key and if your key now starts the car, changing the batteries won't affect that.

Newer 210's do not use a blade for the ignition lock. It is all electronic. That's what you are worried about, needlessly.

The owner's manual - DOH! I can't believe I didn't try that first, I guess I just assumed that MB would not make it that easy. I located the directions in the manual and opened the remote, now I just need to make a trip to Radio Shack and I'm back in business. Thanks for the assist!