Depending on the year of your MB. I suggest you go to You Tube and you search "replace Key FOB for Mercedes Benz" and you will be able to find video instructions on how to proceed. It's that simple 😊!
After reading your message a few times, we think you're talking about needing a new battery in your remote. If so, it is inside of the remote. If this is what you're thinking, what year and model is your Mercedes?
Key's are made at Mercedes ONLY, Battery are located in front engine bay right side, or REAR passager trunk
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