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Mercedes-Benz C-Class: How to Replace SmartKey Battery

Installing replacement batteries inside your key fob requires just a few simple steps. Continue reading to learn how to do it properly.

By Charlie Gaston - May 12, 2015

This article applies to the Mercedes-Benz C-Class w204 (2007-2014).

If your Mercedes-Benz C-Class is warning you that it's time to replace the battery in your key fob, here are easy-to-follow instructions that you will need to complete the process. Before you get started, you will need to grab your key fob and a set of replacement batteries, which you can purchase from any auto parts store, large big box retailer, or by simply going online. You won't need any special tools, but you should complete this DIY project in an area where there is sufficient lighting because you need to locate parts of the key fob that are small. Also, you will need to remove the old batteries without damaging the inside of the key fob.

Materials Needed

  • Key fob
  • Replacement batteries
  • Flat head screwdriver or blade

Step 1 – Remove the valet key

Slide the lever on your key fob to the left, and remove the valet key. Using the valet key, hook and then slide the slider that is located inside of the cavity (towards the notched side of the fob). Press in on the chrome portion of the key fob as you pry out the battery holder by hand.

  • Figure 1. This is what the valet key looks like.
  • Figure 2. The slider is located inside the cavity.
  • Figure 3. Push in on the chrome portion.
  • Figure 4. You will be left with three parts.

Step 2 – Remove the batteries

Now that the battery assembly has been removed, slide out the batteries and replace them using your new set of lithium coin cell batteries.

  • Figure 5. The batteries slide out easily.
  • Figure 6. OE parts are Panasonic CR2025 (3V) X2.

Pro Tip

You may need to pry out the batteries using a flat head screwdriver or blade. However, only apply minimum force and remove the batteries gently.

Step 3 – Reassemble the key fob and test the power

Insert the battery assembly back into the key fob. Use its shape as a guide until you hear a click. Slide the valet key back in, and you are done.

Pro Tip

Generally speaking, most C-Class owners enjoy about four to six years of use before needing to replace the batteries in this key fob. Be sure to always replace old batteries with fresh ones.

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