How to Change a Mercedes Key Fob Battery (CR2025 vs CR2032)
The right battery for a Mercedes key depends on the model, not just the year: the operator’s manuals we read call for a CR 2025 in the C-Class, GLC, GLA, CLA and GLS, and a CR 2032 in the E-Class and the 2018 S-Class. Both are 3 V lithium coin cells, they look almost the same, and they are not interchangeable in the tray. The change itself takes a few minutes and uses the mechanical key hidden inside the SmartKey as the tool, but the cell is a swallowing hazard, so read the safety section first.
Below is what the Mercedes-Benz owner’s manuals actually say for each model they cover, the release steps for both tray styles, and what to do when the dashboard shows “Replace Key Battery.” Where we could not find an official statement, we say “check your manual” instead of guessing.
Types of Mercedes Key Fobs and Their Batteries
Mercedes-Benz’s manuals call every one of these a SmartKey, and treat KEYLESS-GO as a function of the key (hands-free locking and push-button starting), not a separate key. Nicknames such as “chrome key” or “classic key” are common online, but the manuals we read never use them, so we do not sort keys by nickname here. Sort by what is printed on your old cell, or by your model in the table.
| Model | Operator’s manual year read | Cell the manual calls for |
|---|---|---|
| C-Class Coupe (AMG Black Series) | 2012 | CR 2025 |
| C-Class Coupe | 2014 | CR 2025 |
| C-Class Sedan | 2016, 2017, 2018 | CR 2025 |
| C-Class Cabriolet | 2018 | CR 2025 |
| GLC SUV and GLC Coupe | 2017 | CR 2025 |
| GLA | 2018 | CR 2025 |
| CLA | 2018 | CR 2025 |
| GLS | 2017 | CR 2025 |
| S-Class Sedan | 2017 | CR 2025 |
| S-Class Sedan | 2018 | CR 2032 |
| E-Class Sedan | 2017, 2018 | CR 2032 |
| E-Class Wagon | 2017 | CR 2032 |
| CLS | 2010 | CR 2025 “or equivalent”; manual says replace both batteries |
The year-only rule does not hold. Plenty of guides say old plastic keys take two CR2025 cells and newer chrome keys take one CR2032. The manuals say otherwise: the C-Class manuals from 2012 to 2018 each call for a single CR 2025, and the S-Class changes cell between its 2017 and 2018 manuals (CR 2025, then CR 2032). The only manual we read that mentions more than one cell is the 2010 CLS, which says to replace both batteries.
We could not retrieve official manuals for 2019 and newer models in this session, and the GLE and 2018 GLC files were not available at the addresses we tried. For those, check your manual or the number printed on your old cell. You can look up your own model in the Mercedes-Benz USA owner’s manuals library.
Best CR2032 Pick for Mercedes Keys
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Key Fob Replacement Batteries for Mercedes-Benz, CR2032, Pack of 2 The listing names the cell type in its title, so you can match it to the number your manual or your old battery shows.
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As an Amazon Associate we earn from qualifying purchases. This pick is based on the product listing, not hands-on testing. Buy the cell that matches your key, not the one that is cheapest.
Signs Your Mercedes Key Fob Battery Needs Replacing
Mercedes-Benz gives you a built-in test. Press the lock or unlock button on the SmartKey: per the manuals, the battery check lamp on the key lights up briefly when the battery is working, and does not light when it is discharged. If you test it within signal range of the car, the press also locks or unlocks the vehicle, so do the test away from the car if you want to avoid that.
- The check lamp stays dark when you press lock or unlock (the manual’s own test for a discharged battery).
- The key will not lock or unlock the car. The manuals list a discharged or nearly discharged battery first, and strong radio interference second.
- A “Replace Key Battery” message in the instrument display. The manuals list this message as a discharged SmartKey battery.
- Shorter range or repeated button presses. This is a common symptom drivers report, but Mercedes-Benz does not give a range figure or a battery lifespan in the manuals we read, so we do not quote one.
If the key will not lock or unlock the car, the manuals say to use the mechanical key in the door while you sort out the battery. The next step is the cell itself.
Tools and Child Safety Before You Open the Key
You need one replacement cell of the type your manual calls for, a lint-free cloth, and the mechanical key that lives inside the SmartKey. Per the manuals we read, the mechanical key is what releases the battery cover, so no screwdriver is required. Use a pry tool only if your own manual says to.
Safety warning: coin and button cells are dangerous if swallowed. Mercedes-Benz’s own manuals carry a warning that batteries contain toxic and corrosive substances and that swallowing one can cause serious health problems, with a risk of fatal injury, and to keep batteries out of children’s reach. The U.S. Consumer Product Safety Commission says these batteries can burn through a child’s throat or esophagus in as little as two hours, and names keyless entry remotes among the products that use them. See the CPSC announcement for the figures.
- Never leave the old or new cell loose. Do the swap away from children and pets and put the old cell somewhere out of reach right away.
- If a child may have swallowed one, go to the emergency department immediately. Call the National Battery Ingestion Hotline at 800-498-8666 or the Poison Help Line at 800-222-1222 on the way, and have the battery number ready if you can. Do not induce vomiting.
- Do not wait to see if symptoms appear. The National Capital Poison Center says immediate treatment decreases severity and explains the honey guidance for lithium coin cells at poison.org/battery. Never delay the trip to the emergency room to give honey.
- Dispose of the old cell properly. The manuals say not to put it in household rubbish and to take it to a qualified workshop or a battery collection point. The GLC manual adds that SmartKey batteries contain perchlorate, which may need special handling.
Step-by-Step Guide to Changing a Mercedes SmartKey Battery
The manuals show two tray styles. Find your model in the table above, then follow the matching set. If your model is not listed, use the instructions in your own manual, because the cover and tray can differ by key generation.
Keys that use a CR 2025 (C-Class, GLC, GLA, CLA, GLS manuals)
These steps follow the 2012 C-Class Coupe and 2017 GLC Coupe manuals.
- Take out the mechanical key. Push the release catch on the SmartKey and pull the key out.
- Open the battery cover. Press the mechanical key into the opening in the SmartKey, in the direction of the arrow, until the battery compartment cover opens. Do not hold the cover shut while you do this.
- Remove the cover and then tap the SmartKey against your palm repeatedly until the battery falls out. Do not dig at the cell or touch the circuit board.
- Fit the new CR 2025 with the positive terminal facing up. Handle it with a lint-free cloth and make sure its surface is free of lint, grease and other contamination.
- Close it up. Insert the front tabs of the cover into the housing first, then press it closed, and slide the mechanical key back in.
- Test every button on the SmartKey at the vehicle.
Keys that use a CR 2032 (E-Class and 2018 S-Class manuals)
These steps follow the 2017 E-Class manuals and the 2018 S-Class manual. The 2018 E-Class manual adds a sliding step for the cover.
- Remove the mechanical key by pressing the release knob and pulling the key out.
- Open the cover. Press the release button down fully and remove cover 1 (on the 2018 E-Class you slide the cover in the arrow direction, fold it out and remove it).
- Pull out the battery compartment (the small tray) and take out the discharged cell.
- Insert the new CR 2032 into the tray, matching the positive pole marking in the tray and on the battery.
- Push the tray back in until it seats, then put the cover back so that it engages.
- Replace the mechanical key and test the buttons at the car.
Two habits worth keeping on either type: use the cell number your manual gives, and do not touch the circuit board or contacts. None of the manual procedures asks you to go near them.
Does a Mercedes Key Need Programming After a Battery Change?
In the manuals we read, the procedure ends with checking that the SmartKey buttons work at the vehicle. None of them lists a reprogramming or resync step after a battery change. One seller’s listing for the pack in our pick says no programming is required, but that is the seller’s claim, not Mercedes-Benz’s. Many guides mention a “resync sequence” for Mercedes keys; we found none in the official manuals and removed that advice from this page.
If the key still does nothing after the swap, check in this order: the cell number matches your manual, the positive side faces the way your manual shows, the cell surface is clean, and there is no strong radio interference nearby (the manuals list this as a separate cause of a key that will not lock or unlock). If it still fails, see a qualified workshop. Our page on why a car says “key not detected” covers the other common causes.
Dealer vs DIY: Who Should Change the Battery?
Mercedes-Benz’s own wording, repeated in every manual we read, is that it recommends having the SmartKey battery replaced at a qualified specialist workshop. The same manuals also print the DIY steps and say you can get the battery at a qualified specialist workshop. So both routes are sanctioned; the workshop route is the one the maker recommends.
- DIY makes sense if you know your cell number, can work out of the reach of small children, and your manual shows the same tray style as the steps above.
- Use a workshop if the cover will not release without force, you cannot confirm the cell type, your key was damaged, or the key still fails after a correct swap.
- On cost: we could not verify dealer pricing from an official source, so we do not quote a number. Ask your Mercedes-Benz center for a price before you decide.
Not driving a Mercedes? Our general guide on how to open a car key fob covers other makes, and our car key battery replacement guide lists the general method.
FAQs
What battery does a Mercedes key fob use?
It depends on the model. The operator’s manuals we read call for a CR 2025 in the C-Class (2012 to 2018), GLC (2017), GLA and CLA (2018), GLS (2017) and 2017 S-Class, and a CR 2032 in the E-Class (2017 and 2018) and the 2018 S-Class. Check your own manual or the number printed on the old cell.
How do I open a Mercedes key to change the battery?
Remove the mechanical key from the SmartKey first. On the C-Class and GLC style keys, you then press the mechanical key into the opening in the direction of the arrow until the battery cover opens. On the E-Class and 2018 S-Class style keys, you press the release button to remove the cover and pull out the battery tray.
Do I need to reprogram a Mercedes key after changing the battery?
The manuals we read list no reprogramming step: the last step is to check that all SmartKey buttons work at the vehicle. If the key does not work after a correct battery swap, see a qualified workshop.
What does “Replace Key Battery” mean on a Mercedes?
The manuals list it as the SmartKey battery being discharged, with the instruction to change the battery. Until you do, lock and unlock with the mechanical key if the buttons stop working.
Is a key fob battery dangerous for children?
Yes. Coin and button cells can burn through a child’s esophagus in as little as two hours, per the CPSC. If a child may have swallowed one, go to the emergency department immediately and call 800-498-8666 or 800-222-1222 on the way.
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