How to Change the Battery in a Mercedes Key Fob

The main difference is the type of key fob you have:

• Chrome SmartKey® – newer metal-style key.
• SmartKey® (plastic) – older, all-plastic key.
• Other newer fobs – very similar steps, just slightly different shapes.

Below, you’ll find out how to identify your key, which battery you need, and step-by-step instructions to change it safely.

Step 1: Identify Your Mercedes Key Fob Type

Before anything else, look closely at your key fob. Mercedes models typically feature two main types: the older SmartKey® and the newer Chrome SmartKey®.

Older SmartKey® (Plastic)

• The body is mostly plastic.
• Buttons may be black rubber with symbols for lock, unlock, and panic.
• No shiny metal casing around the outside edge.

If your key looks more like simple black plastic, it is likely the older SmartKey®.

Chrome SmartKey® (Newer Metal-Style)

• The outside has a metal or chrome-looking frame.
• It feels a bit heavier and more premium in the hand.
• Often has a silver tab or latch at the bottom for the emergency key.

The steps for changing the battery are basically the same across both the older and newer Chrome Key variations.

Very New Styles

Some very new models have slightly updated key fob shapes. Even so, the process is still:

• Remove the small emergency key blade.
• Open the battery cover using the key or a plastic tool.
• Swap the coin battery and reassemble.

If your key looks different from the examples here, you can still follow the same general idea and check your owner’s manual for diagrams.

Step 2: Choose the Right Battery

Most Mercedes key fobs use one of these:

• CR2025 coin battery – the most common type.
• CR2032 coin battery – used in some newer or different designs.

Typical combinations (always double-check yours):

• Older SmartKey® (plastic): usually two CR2025 batteries.
• Chrome SmartKey® (newer metal-style): usually one CR2025 battery.

The safest method is to open the fob once, check the exact code printed on the old battery, and buy the same type from a good brand.

Step 3: How to Change the Battery in a Chrome SmartKey®

These are the newer, metal-looking keys. Here’s the basic method:

What You Need

• 1 × new CR2025 (or the type printed on your old battery).
• Clean hands or a small cloth.
• Optional: plastic trim tool or very small flathead screwdriver (if needed).

Chrome SmartKey® Battery Replacement Steps

1. Remove the emergency key.
   On the bottom of the fob, pull or slide the small silver tab. At the same time, pull the metal key blade out of the fob.
2. Open the battery cover.
   Where the key came out, you’ll see a small gap or slot. Insert the narrow end of the emergency key (or a small plastic tool) into that slot and gently twist or push to pop the cover off.
3. Remove the old battery.
   Note which side is facing up (usually the “+” side faces up). Then carefully lift the battery out with your fingernail or a plastic tool.
4. Insert the new battery.
   Place the new CR2025 battery into the space with the same orientation as the old one (the + side up if that’s how it was before).
5. Close the cover.
   Snap the battery cover back into place. Press around the edges gently until it clicks and sits flat.
6. Reinsert the emergency key.
   Slide the metal key back into its slot until it clicks.
7. Test the key.
   Stand near your car and press lock/unlock. If the lights flash or doors respond, you’re done.

If the buttons do nothing, check that the battery is the correct type and the polarity (plus and minus) matches the original.

Step 4: How to Change the Battery in an Older SmartKey® (Plastic)

Older SmartKey® fobs look simpler and are usually all plastic. They often use two CR2025 batteries stacked in a small tray.

What You Need

• 2 × new CR2025 batteries (if your old ones are CR2025).
• Clean hands or small cloth.

SmartKey® Battery Replacement Steps

1. Remove the emergency key.
   On the back or end of the key fob, find the sliding latch. Pull or slide the latch while pulling the metal key blade out of the fob.
2. Open the battery compartment.
   Insert the key blade horizontally into the slot that appears and gently push. This releases or lifts the small battery tray or compartment.
3. Remove the battery tray.
   Carefully pull the tray out. You should see the two coin batteries inside.
4. Note the battery orientation.
   Look at which way the “+” side is facing. If needed, take a quick photo so you remember the correct order.
5. Replace the batteries.
   Remove the old batteries and insert the new ones in the same orientation (plus and minus exactly the same as before).
6. Reinstall the tray.
   Slide the battery tray back into the key fob until it clicks into place.
7. Reinsert the emergency key.
   Slide the metal key blade back into its slot until it locks.
8. Test the fob.
   Try lock/unlock on your car. If it works, your battery change was successful.

Step 5: Generic Method for Other Mercedes Key Fobs

Some very new key fobs may not look exactly like the SmartKey® or Chrome SmartKey®, but they still follow almost the same pattern:

1. Press the small button or latch and remove the metal emergency key.
2. Use the key or a plastic tool to gently pry open the back cover where the key came out.
3. Remove the old battery, noting which side is up.
4. Insert a new coin battery of the same type (CR2025 or CR2032) with the same orientation.
5. Snap the cover back on and reinsert the metal key.
6. Test the lock/unlock functions near the car.

If you ever feel unsure, your owner’s manual has small pictures showing exactly where the slots and tabs are.

Signs Your Mercedes Key Fob Battery Is Low

Common warning signs that it’s time to change the battery include:

• You have to stand closer and closer to the car for the buttons to work.
• The car sometimes does not lock or unlock on the first press.
• A message appears on the dashboard like “Key Battery Low” or “Replace Key Battery.”
• The car has trouble detecting the key for push-button start.

If you see these signs, changing the battery early can save you from getting stuck outside the car.

Tips for a Smooth and Safe Battery Change

• Use good-quality batteries. Well-known brands last longer and are more reliable.
• Avoid metal tools directly on the battery if possible, to prevent short circuits.
• Do not force anything. If a cover will not open, look again for a latch or slot – the force needed is small.
• Keep track of polarity. “+” and “−” must match the original layout or the key will not work.
• Dispose of old batteries properly. Use a battery recycling box or local collection point.

When You Should Visit a Mercedes Dealer or Specialist

Changing the key fob battery is usually simple, but sometimes you still need professional help. It’s a good idea to visit a dealer or specialist if:

• The key fob still does not work at all after fitting a fresh battery.
• The dashboard continues to show “Replace Key Battery” even with a new battery.
• The fob has been dropped in water or physically damaged.
• You think the fob may need reprogramming to sync with the car.

In these cases, they can test the key, check the signal, and repair or replace it if needed.

Quick Summary

• Most Mercedes key fobs use CR2025 or CR2032 coin batteries.
• Older SmartKey® (plastic) usually takes two CR2025 batteries.
• Newer Chrome SmartKey® usually takes one CR2025.
• The basic steps are: remove emergency key → open cover → swap battery → close cover → test.

Once you’ve successfully completed the process one time, changing a Mercedes key fob battery becomes a quick, simple job you can repeat whenever the range drops or the car warns you about a low key battery.