These instructions apply to the Mercedes GLC Mk1 (X253) 2015-2022.
For other models, please choose your vehicle here.
If the SmartKey for your Mercedes-Benz GLC (X253, 2015–2022) only unlocks the car when you are almost touching the door, or KEYLESS-GO has stopped waking the car as you approach, the coin cells inside the fob are almost certainly flat. The X253 — whether it left the factory with the standard remote SmartKey or the KEYLESS-GO version — uses the same flat, chrome-trimmed one-piece key that debuted on the W205 C-Class. That key is the reason so many owners buy the wrong battery: unlike most rivals it does not take a single CR2032. It takes two coin cells, stacked. Here is exactly what to buy, how to open the key without cracking the case, and why a replacement key is the one part of this job you cannot do at home.
How to Tell the Fob Battery Is Dying
- Shrinking range. You have to stand right next to the GLC — or hold the key against the door handle — before it will lock or unlock. This is the first and most reliable warning.
- KEYLESS-GO gets lazy. On KEYLESS-GO cars the door no longer unlocks as you grip the handle, and the push-button start needs the key held close to the start button or dropped into the cup holder to work. That is a weak cell, not a failed system.
- A dash message. The instrument cluster shows a “Key battery low” style warning when the SmartKey reports low voltage — treat it as a prompt to change the cells within a week or two, not an emergency.
- Cold-morning dropouts. Lithium coin cells lose punch in the cold, so intermittent cold-weather misbehaviour points at the battery.
A pair of cells in an X253 key typically lasts two to three years. KEYLESS-GO keys drain faster than the plain remote because the key is constantly listening for the car. If yours is a couple of years old and showing any of the above, fit fresh cells before you suspect the car.
The Battery You Need
The X253 SmartKey takes two CR2025 3-volt lithium coin cells — not one, and not the thicker CR2032 that fits many other brands. Both cells go in together, stacked in the same compartment. Buy them as a matched pair and replace both at once; mixing an old cell with a new one leaves you with the range of the weaker one. The CR2025 is sold in any supermarket or hardware shop, so there is no need to visit a dealer for the part. Choose a reputable brand — cheap cells sag under the brief high current the transmitter draws.
How to Change the Battery in the GLC X253 SmartKey
- Release the emergency key. Slide the small catch on the side of the fob in the direction marked and pull the mechanical key blade straight out of the body. Set it aside — you will use it as a lever, and you will need it to get into the car if the cells are already dead.
- Pop off the battery cover. Look at the back of the key for the small recess the blade left behind. Press the tip of the emergency blade into that slot and lever gently to release the button-cell cover, then lift it away. It unclips — there is no screw and no need to force the two chrome halves of the shell apart.
- Note the orientation, then lift the cells out. The two CR2025 cells sit stacked. Ease them out with a fingernail or the blade tip, taking care not to bend the thin contact spring beside them — a splayed spring is a common cause of a “dead” key after a battery change.
- Fit the new pair. Drop in both fresh CR2025 cells with the positive (+) side facing up — the flat face carrying the CR2025 marking should be visible as they sit in the tray. Match the orientation of the cells you removed if in any doubt.
- Reassemble. Press the cover back on until it clicks flush, then slide the mechanical key blade back into the body until it latches. Test all the buttons and, on KEYLESS-GO cars, walk up and try the handle.
⚠️ Get the polarity right and use two cells. Both CR2025s must go in the same way up, positive face upward, and the compartment genuinely needs the pair — a single cell will not give 3 volts to the transmitter properly and the key will behave as if the battery is still flat. Copy the orientation of the cells you took out and you cannot go wrong.
Confirm It Worked
Stand back a few metres and lock, then unlock, the GLC. Full range should return the instant the fresh cells seat. On KEYLESS-GO cars, confirm the door unlocks as you grip the handle and that the car starts on the button without holding the key close. Any “key battery low” message clears the next time the car reads a healthy key — sometimes immediately, occasionally after one short drive.
If a Fresh Cell Doesn’t Fix It
- Confirm you fitted two cells, both positive-up. This is the single most common mistake on the X253 key — one cell, or a cell in upside down, mimics a completely flat key.
- Check the contact spring. If it was bent flat while prising the old cells out, it may not be touching the new stack; ease it back so it presses firmly.
- Wipe the contacts. Finger grease or light corrosion on the terminals is enough to cause dropouts — clean them with a dry cloth.
- Try the spare key. If the second key works perfectly on fresh cells and the first still will not, the problem is that fob’s electronics, not the car.
- Rule out the car’s own battery. A weak 12 volt battery in the GLC can make the car slow to respond to any key; if the car is also cranking lazily, that is a separate issue worth checking.
New Key or Spare — Why It’s a Dealer Job
Changing the cells keeps the key’s existing coding, so nothing needs re-pairing — the fob works the moment the cover clicks shut. Cutting and coding a new key is a different matter. Mercedes SmartKeys are tied to the car’s FBS (drive authorisation) system, and a blank has to be ordered against the VIN and married to the car with factory-level equipment, usually needing proof of ownership. That makes it a main-dealer job. The practical takeaway: keep the cells in your spare key fresh too, so you are never down to a single working key.
Frequently Asked Questions
What battery does a Mercedes GLC X253 key take?
Two CR2025 3-volt lithium coin cells, fitted as a stacked pair. Do not substitute a single CR2032 — the X253 key is designed around two of the thinner CR2025 cells.
Does the GLC key really need two batteries?
Yes. The flat chrome SmartKey used across the X253 range holds two CR2025 cells together. Fitting only one leaves the transmitter under-powered, and the key behaves as though the battery is still flat.
Which way up do the cells go?
Both go in with the positive (+) face upward — the side stamped CR2025 visible as they sit in the tray. Always match the orientation of the cells you removed.
Do I need to reprogram the key after changing the batteries?
No. A battery swap does not touch the key’s coding, so it works straight away. Only a brand-new key needs coding to the car.
How long should the GLC key battery last?
Roughly two to three years. KEYLESS-GO keys drain faster than the plain remote because they are always listening for the car, so expect the shorter end of that range if your GLC has keyless entry.
Can I still start the GLC if the key battery is completely dead?
Yes. Use the emergency blade hidden in the fob to unlock the driver’s door, then hold the SmartKey against the start button (or place it in the marked slot or cup holder if fitted) to start the car — the system reads the key over a short range even with dead cells, so a flat battery will not strand you.
If your GLC threw a warning or the remote died suddenly right after the 12 volt battery was disconnected — rather than fading gradually — the cause is more likely a stored fault than the coin cells. You can look up what a logged code means on autodtcs.com before spending money on a new key.
Independent guide — not affiliated with Mercedes. Always follow your official service manual and safety precautions. Read our full disclaimer.