Changing the battery in your Mercedes key is something you can usually do yourself in just a few minutes. Most Mercedes keys (key fobs) use small coin batteries like CR2025 or CR2032, and the process is very similar across most models.
The exact steps depend slightly on the type of key you have:
- Chrome SmartKey – newer key with a shiny metal frame.
- Plastic SmartKey – older, all-plastic style key.
- Very new keys – similar method, just a slightly updated shape.
Below, you will learn how to:
- Identify which key you have.
- Find the correct battery type.
- Change the battery step by step for each key style.
- Avoid common mistakes and problems.
Step 1: Identify Your Mercedes Key Type
Take a close look at your key. Mercedes uses a few main designs. Knowing which one you have makes the instructions easier to follow.
1. Chrome SmartKey (Newer Style)
This is the more modern key that many recent Mercedes models use. It usually has:
- A shiny chrome or metal-looking frame around the key.
- Smooth, rounded shape that feels a bit heavy in your hand.
- A small metal key blade hidden inside, which you can pull out with a tiny latch.
If the outside edge of your key looks metallic and polished, you most likely have a Chrome SmartKey.
2. Plastic SmartKey (Older Style)
The older SmartKey is mostly plastic and looks a little simpler:
- Body is black plastic without a shiny metal frame.
- Buttons may be rubber, with icons for lock, unlock, and panic.
- Also has a hidden metal emergency key you can remove with a latch.
If your key feels lighter, mostly plastic, and not chrome-framed, this is probably your key type.
3. Very New Key Designs
Some very new Mercedes models have a slightly updated key shape, but the battery change steps are almost the same:
- Remove the metal emergency key.
- Use the gap you exposed to open the battery cover.
- Swap the coin battery, then reassemble.
Even if your key looks a bit different, you can follow the same logic and adjust slightly as needed.
Step 2: Find the Right Battery Type
Most Mercedes keys use one of these coin batteries:
- CR2025 – very common in Mercedes keys.
- CR2032 – used in some newer or different key shapes.
Rough guide (always check your old battery to be sure):
- Chrome SmartKey: usually uses one CR2025.
- Older Plastic SmartKey: usually uses two CR2025 stacked in a small tray.
The safest way to be sure:
- Open the key once.
- Look at the code printed on the old battery (for example, “CR2025”).
- Buy the same type from a good battery brand.
Step 3: Change the Battery in a Chrome SmartKey (Newer Metal Style)
If your key has a shiny metal frame, follow these steps. The process is gentle and quick if you do it slowly.
What You Need
- 1 × new CR2025 (or the battery type printed on your old one).
- A small cloth or tissue (optional, to avoid fingerprints on the battery).
- A plastic tool or the metal key itself to open the cover.
Steps for Chrome SmartKey
- Remove the emergency key blade.
On the bottom end of the key, find the small release button or slider.
Press or slide it, then pull the metal key blade out of the fob. - Open the battery cover.
Look at the opening where the key blade came out.
You should see a small slot or notch inside.
Insert the narrow tip of the metal key or a plastic tool into this slot and gently twist or push to pop the back cover off. - Remove the old battery.
Note which side of the battery is facing up (usually the “+” side is visible).
Carefully lift the battery out with your fingernail or a plastic tool. - Insert the new battery.
Place the new battery into the same spot with the same orientation as the old one
(normally “+” side up). Make sure it sits flat and snug. - Close the battery cover.
Align the cover with the key fob and press it back into place until it clicks.
Run your finger around the edges to check it is fully seated. - Put the emergency key back.
Slide the metal key blade back into its slot until it clicks into place. - Test the key.
Stand near your car and press the lock and unlock buttons.
If the lights flash or doors respond, the battery change worked.
If nothing happens, double-check that:
- The battery is the correct type.
- The “+” and “−” sides are the right way around.
- The cover is clicked fully into place.
Step 4: Change the Battery in a Plastic SmartKey (Older Style)
Older plastic SmartKey fobs often use two CR2025 batteries stacked in a tray.
The opening method is slightly different, but still easy.
What You Need
- 2 × new CR2025 batteries (if that is what your old ones are).
- A small cloth or clean hands.
Steps for Plastic SmartKey
- Remove the emergency key blade.
Find the small release latch at the end or back of the key.
Slide or pull it, then pull the metal key blade out of the fob. - Release the battery tray.
Look into the key where the blade came from.
Insert the key blade or a small plastic tool horizontally into the slot there and gently push.
This should pop out or release the battery tray. - Pull out the battery tray.
Carefully slide the tray completely out of the key.
You should now see the two small coin batteries inside. - Note the battery orientation.
Before removing anything, look closely at how the batteries are stacked.
Check which side of each battery faces up (and if needed, take a quick photo). - Remove the old batteries.
Gently lift out the two old CR2025 batteries. - Install the new batteries.
Place the new batteries into the tray in the same order and orientation as the old ones.
The “+” and “−” sides must match exactly. - Reinsert the battery tray.
Slide the tray back into the key fob until it clicks and sits flush. - Put the emergency key back.
Slide the metal key blade back into its slot until it locks into place. - Test the key.
Try locking and unlocking your car. If it works, you are finished.
If the car does not respond, check that both batteries are new, correctly stacked, and the tray is fully seated.
Step 5: Generic Method for Very New Mercedes Keys
If your key looks very modern and slightly different, do this:
- Press the small button or slider and remove the metal emergency key.
- Use the gap to gently pry off the back cover (with the key tip or a plastic tool).
- Note which way the old battery is facing, then remove it.
- Insert a new coin battery of the same type with the same orientation.
- Snap the cover back on and reinsert the emergency key.
- Test the buttons near your car.
The pattern is always: remove blade → open cover → swap battery → close cover → test.
How to Know When Your Key Battery Is Low
Your Mercedes key will usually warn you before the battery is completely dead. Common signs include:
- The car only locks or unlocks when you stand very close.
- You need to press the buttons several times before it responds.
- A message appears in the car, such as “Key Battery Low” or “Replace Key Battery.”
- Push-button start sometimes says it cannot detect the key (even when it is in the car).
Once you notice these signs, it is a good idea to replace the battery soon so you are not caught out.
Tips for a Smooth Battery Change
- Use good-quality batteries. Cheaper, unknown brands may not last as long.
- Avoid scratching the battery. If possible, use a plastic tool instead of metal screwdrivers.
- Keep track of polarity. The “+” side of the battery must match the way it was originally.
- Do not force anything. Mercedes key covers and trays open with light pressure. If it feels stuck, check for a hidden latch.
- Dispose of old batteries properly. Use a battery recycling bin or local collection point.
When to Get Help from a Dealer or Specialist
Most battery changes are easy, but sometimes you may still need help. You should visit a dealer or specialist if:
- The key still does not work after fitting a fresh battery.
- The car keeps showing a “Replace Key Battery” message even with a new battery.
- The key has been damaged by water or a heavy impact.
- You suspect the key might need reprogramming or there is an issue with the car’s receiver.
They can test the key, check the signal, and program or replace it if needed.
Quick Summary
Changing the battery of a Mercedes key is simple once you know the steps:
- Most keys use CR2025 or CR2032 coin batteries.
- Chrome SmartKey: usually one CR2025 and a pop-off back cover.
- Plastic SmartKey: usually two CR2025 in a pull-out tray.
- The basic process: remove the emergency key → open the cover or tray → swap the battery → close and test.
Once you have done it once, you will find that replacing your Mercedes key battery is a fast and simple job you can handle yourself whenever the “key battery low” warning appears.
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