These instructions apply to the Smart Forfour Mk2 (W453) 2014-2021.
For other models, please choose your vehicle here.
When the remote on a Smart ForFour (W453, 2014–2021) starts working only from close up, flashes weakly, or stops responding altogether, the coin cell inside the key is almost always the culprit. Because the W453 was engineered alongside the third-generation Renault Twingo and built on the same platform, its keys are Renault hardware too — and that matters when you open one up. Early W453 cars left the factory with a small fixed “original-style” remote, but within roughly the first year Smart switched to the familiar Renault folding “flip” key with a spring-out metal blade. The two keys take different coin cells and open in completely different ways, so the first job is to identify which one is in your hand.
How to Tell the Fob Battery Is Dying
- Shrinking range. You have to stand right next to the ForFour — or almost touch the fob to the door — before it will lock or unlock. This is the classic first warning and usually the earliest one you notice.
- The button LED dims or stops flashing. On both W453 key styles the little indicator light blinks when you press a button; once it goes faint or dark on a press, the cell is nearly flat. It is the quickest way to confirm the fault is in the key, not the car.
- Buttons respond only sometimes. Intermittent locking, especially on cold mornings, is a tired cell that can no longer supply the brief burst of current the transmitter needs at low temperature.
- You are pressing twice. Needing a second or third press to get a reaction is a cell on its way out.
A coin cell in a W453 remote typically lasts two to four years. If yours is around that age and showing any of the signs above, fit a fresh cell before you start suspecting the receiver or the immobiliser.
The Battery You Need
It depends on which key you have:
- Folding “flip” key (the common Renault-style remote with a blade that springs out of the body): a single CR2032 3-volt lithium coin cell.
- Early original-style key (a smaller fixed remote, fitted to the first W453 cars): a single CR2016 3-volt lithium cell — same diameter as a CR2032 but half the thickness, so the two are not interchangeable.
Both are cheap, common cells sold in any supermarket or hardware shop. Buy a good-quality branded cell — budget cells can sag under the short high-current pulse the transmitter draws and give poor range even when they read as “new.” If you are unsure which key you have, the safest move is to open it and match the code printed on the cell you take out.
Method 1 — Folding “Flip” Key (CR2032)
- Fold the metal blade closed so the key is easier to grip.
- Find the seam that runs around the edge of the case. Push a flat plastic tool, a small flat-blade screwdriver or a coin into the gap and gently twist to pop the two halves apart. Work your way round the seam rather than forcing one spot.
- Lift the halves open. The CR2032 stays clipped into one half and makes contact with the circuit board through a set of prongs and a gold pad — note how it sits before you disturb it.
- Ease the old cell out. Fit the new CR2032 with the positive (+) side facing down into its clip, matching the orientation you just noted.
- While the key is open, wipe the contact prongs and gold pad with a dry cloth — grease or light corrosion there is a common cause of dropouts.
- Line the halves up and press them firmly together until the seam clicks shut all the way round, then test every button.
Method 2 — Early Original-Style Key (CR2016)
- Turn the key over and look for the small retaining screw on the back.
- Undo it with a fine cross-head (Phillips) screwdriver and keep the screw somewhere safe — it is tiny.
- Separate the two halves of the case; if they do not part freely, ease the seam with a flat plastic tool.
- Note which way the old cell sits, lift it out, and drop the fresh CR2016 in the same orientation you removed the old one.
- Refit the cover, drive the screw back in snugly — do not overtighten, the housing is plastic — and check the buttons.
⚠️ Get the polarity right. A coin cell fitted upside down will not power the remote and can slowly discharge against the contacts. On the flip key the correct orientation is positive-side-down; on the original-style key, always copy the way the cell you removed was sitting rather than guessing.
Did It Work?
Stand back a few metres and lock, then unlock, the ForFour. Full range should return straight away and the button LED should flash brightly again. If the remote seems slightly out of step after the swap, press a button a couple more times within range of the car — the key re-syncs with the receiver after a few operations.
If a Fresh Cell Doesn’t Fix It
- Re-check polarity and seating. An upside-down or loose cell is by far the most common reason a “new” battery does nothing. Make sure it clicks firmly under its clip against clean contacts.
- Clean the contacts. Wipe the prongs and gold pad inside the key; a smear of finger grease is enough to cause intermittent range.
- Confirm the cell is genuinely fresh. A CR2032 or CR2016 that has sat in a drawer for years can be half-flat out of the packet — a cheap coin-cell tester or a multimeter should read close to 3 volts.
- Still nothing? If the LED will not light with a known-good cell, the transmitter itself may have failed, which is rare compared with a simple flat or wrong-way cell. Rarely, a weak car 12 V battery can mimic key faults if the ForFour is slow to wake.
New Key or Spare — Why It’s a Dealer Job
Changing the coin cell leaves the key’s coding untouched, so nothing needs reprogramming and the remote works the moment the fresh battery goes in. A new key is a different story: because the W453 shares Renault’s electronics, a blank key has to be cut to the VA2 blade profile and its transponder coded to the car’s immobiliser with a diagnostic tool — work that has to be ordered against the vehicle’s VIN. That makes adding a spare or replacing a lost key a job for a Smart/Mercedes dealer or an auto-locksmith who handles Renault-based systems. The practical takeaway: keep the battery in your spare key fresh too, so you are never down to a single working remote.
Frequently Asked Questions
What battery does a Smart ForFour W453 key take?
The common folding flip key uses a CR2032 3-volt lithium coin cell. The early original-style remote fitted to the first W453 cars uses a thinner CR2016 instead — check the key you have or read the code off the old cell.
How do I open the ForFour flip key?
Fold the blade away, then push a flat plastic tool or a coin into the seam around the edge and twist gently to split the two halves. There is no screw on the flip key — only the older original-style remote has one.
Which way up does the battery go?
In the flip key the CR2032 sits with the positive (+) side facing down in its clip. On the original-style key, match the orientation of the cell you removed. Fitting a coin cell the wrong way round simply leaves the remote dead.
Do I need to reprogram the key after changing the battery?
No. A battery swap does not affect the key’s coding, so it works immediately. Only a brand-new or replacement key needs coding to the car.
How long should a W453 key battery last?
Usually two to four years. Frequent remote use, or leaving the key close to the car so it is woken often, shortens that.
Can I still get into and drive the ForFour if the fob is completely dead?
Yes. Slide out the mechanical blade in the flip key to unlock the driver’s door manually, then follow the car’s procedure for starting with a flat remote so a dead cell never leaves you stranded.
If the remote died the instant the car’s 12 V battery was disconnected — rather than fading over weeks — the pairing rather than the cell is the more likely suspect, and the car may have logged a fault while it was without power. You can look up what any stored code means on autodtcs.com.
Independent guide — not affiliated with Smart. Always follow your official service manual and safety precautions. Read our full disclaimer.