replace battery in keyfob?
 

i'm getting this message after owning the car for 11 months, how much time do i have before the battery completely dies?

Not sure but if it does you will need to open the car with the metal key in the fob and then put the fob in the holder to start and run.
i usually change batteries no more than a day after getting the message. I have had a dead key before in a c class and i just got the key not recognised message.

I wouldn't delay on that. It's not difficult to do and there's a really good chance that after only 11 months, your dealer parts department will replace it for you without charge.

When you park, turn off your car and lock it, double lock it, by tapping the lock button twice to hear two horn beeps. You'll see the led on the front of your key fob light up for a second. What this does is stop your key fob from constantly looking for the car and it preserves battery life significantly.

do this each time i exit the car or once?

and what size battery does it take?

Yes, every time you lock the car.

The keyfob uses a CR 2032 3V cell battery. Your owners manual details how to replace the battery on page 58.

Really good advice. It stops the key transmitting hence the power saving and therefore protects the key from being cloned as in the video.:)

https://youtu.be/AJb-P7TJFI0

No, it doesn't. The only way to stop the fob from doing it is to double tap the lock button directly on the fob.

Battery is covered under warranty and is replaced at normal service intervals.