I opened/closed the door/trunk 10 times a day on the average (morning to work, lunch, back to work from lunch, liquor store, errands, ...) the battery lasted 6 years 8 months and 3 weeks and a half.No you do not need the key batteries to start the car.
I am an optimist I think the key batteries will last for 500 years!
I needed a new key so I opted for the "buy a Mercedes keyring for £200,and get a free key"......or was it the other way round?The electronics in both of my remotes failed before the batteries ever did.
Just spent 250 + tax for a new key at the stealership. I'm really happy about that.
Kevin, there is still one way your wife might get stuck. If (and this would be a rare coincidence) the batteries die between locking and unlocking the doors you need to tell her how to extract the metal blade key to unlock the driver's door. Once that is open the other replies are correct that the "dead" key will disable the security system and will start the engine.thanks for the tips. I just didn't want the wife to get stuck one day...