These instructions apply to the Peugeot 308 Mk3 (P5) 2021-Present.
For other models, please choose your vehicle here.
When the remote on a Peugeot 308 Mk3 (P51, 2021–present) only locks the car from touching distance, flashes intermittently, or stops responding altogether, the coin cell inside the key has almost certainly gone flat. This third-generation 308 — the first built on Stellantis’ updated EMP2 platform with the new lion badge — ships with one of two keys: a folding “flip” remote as standard, or the optional hands-free (keyless entry & start) smart key that lets you unlock and start with the fob in your pocket. Both take the same battery and both are a five-minute driveway job. Here is the exact cell, how to open each key, and why cutting a brand-new one is the part you can’t finish at home.
How to Tell the Fob Battery Is Dying
- Shrinking range. You have to stand right by the car — or hold the fob against the door handle — before it will lock or unlock. This is the first and clearest sign.
- “Low battery in remote control” message. The 308’s i-Cockpit digital cluster displays a low key-battery warning when the cell is weak; on hands-free cars it may also warn that the key is no longer detected.
- Hands-free access gets unreliable. On keyless cars the door stops unlocking as you approach, or the Start button won’t wake the car until you hold the fob right against the steering column.
- Cold-morning dropouts. A cell that is nearly done struggles in low temperatures, so buttons that worked yesterday go intermittent on a frosty start.
A CR2032 in a 308 remote typically lasts two to four years. If yours is around that age and showing any of the above, fit a fresh cell before you suspect the car’s receiver or immobiliser.
The Battery You Need
Both the folding remote and the hands-free smart key on the Mk3 308 use a single CR2032 3-volt lithium coin cell — a 20 mm button battery sold in any supermarket, hardware shop or petrol station. Note that this is different from the older second-generation 308, whose standard remotes commonly used the smaller CR1620; don’t assume an older spare’s battery matches. As always, the safest check is the code stamped on the cell you take out. Buy a good-quality branded CR2032 — cheap cells sag under the brief high current the transmitter draws and can give poor range even when “new.”
Method 1 — Folding “Flip” Remote
- Press the small chrome release button and let the metal blade spring out, then fold it back closed — this exposes a narrow notch in the recess where the blade normally sits.
- Slip a fine flat-blade screwdriver or a coin into that notch and gently twist to split the two halves of the case apart. Work slowly so you don’t snap the plastic clips.
- Note which way the old cell faces, then lift it out. Fit the new CR2032 with the positive (+) side up, matching the orientation you just removed.
- Press the two halves back together until they click all the way round, and test every button.
Method 2 — Hands-Free (Keyless) Smart Key
- Release the emergency blade first: slide or press the catch and pull the mechanical key blade straight out of the fob body.
- Insert a flat plastic tool (or the emergency blade itself) into the seam the blade leaves behind and gently prise the case apart along its join.
- Ease out the old cell without touching the circuit board’s metal contacts, and drop in the new CR2032 the same way up as the one you removed.
- Click the halves back together and slide the emergency blade home until it latches.
⚠️ Get the polarity right. A coin cell fitted the wrong way round won’t power the transmitter and can quietly discharge against the contacts — so always copy the orientation of the cell you took out rather than guessing.
Check It Worked
Step back a few metres and lock, then unlock, the car; full range should return straight away. On a hands-free 308 the “low battery” message clears once the car next reads a healthy fob — sometimes instantly, occasionally only after a drive cycle. Walk up to the door with the fob in your pocket to confirm keyless detection is back to normal.
If a Fresh Cell Doesn’t Fix It
- Re-check seating and polarity. The cell must sit firmly under its clip, positive side matching what you removed, against clean terminals — a loose or upside-down cell is the most common reason a “new” battery seems dead.
- Wipe the contacts. A film of finger grease or light corrosion on the terminals is enough to cause dropouts; clean them with a dry cloth.
- Try the mechanical override. If the car itself won’t wake, hold the fob directly against the marked spot on the steering column and press Start — the 308 can read the transponder even with a flat cell.
- Still warning after a drive? A weak car 12 V battery can mimic key faults on keyless models; if the 308 is generally slow to wake, have the vehicle battery checked too.
New Key or Spare — Why It’s a Dealer Job
Changing the cell leaves the fob’s existing pairing untouched, so no reprogramming is needed and the key works the moment you reassemble it. A brand-new key is a different matter: the 308’s immobiliser has to be accessed with Peugeot’s diagnostic equipment, and blank hands-free fobs must be ordered against the car’s VIN and coded to it. That makes adding a spare or replacing a lost key a job for a Peugeot dealer or an auto-locksmith — so keep the battery in your spare fresh as well, and you’re never left relying on a single working key.
Frequently Asked Questions
What battery does a Peugeot 308 Mk3 key take?
A single CR2032 3-volt lithium coin cell, used by both the folding remote and the hands-free smart key. Older second-generation 308 remotes often used a CR1620, so check the code on the cell you remove if you’re unsure.
Which way up does the cell go?
On the folding remote the CR2032 sits with the positive (+) side up. Whichever key you have, the reliable rule is to copy the exact orientation of the cell you took out before fitting the new one.
Do I need to reprogram the key after changing the battery?
No. A battery swap doesn’t affect the fob’s coding, so it pairs with the car straight away. Only a completely new key needs programming.
How long should a 308 key battery last?
Usually two to four years. Frequent remote use — or leaving a hands-free fob sitting close to the car so it keeps waking up — will shorten that.
My 308 key still won’t work after a new battery — what now?
Re-check the cell’s polarity and that it’s seated firmly on clean contacts first. If the car still won’t detect it, hold the fob against the steering column and press Start; if that starts the car, the transmitter side of the fob may have failed and need replacing, which is rare compared with a simple flat or misfitted cell.
Can I still drive if the fob battery is completely dead?
Yes. Use the emergency blade hidden in the fob to unlock the driver’s door, then hold the fob against the marked spot on the steering column and press the Start button — the keyless system is designed to read the key this way even with a dead battery, so a flat cell won’t strand you.
If the remote died suddenly right after the car’s 12 V battery was disconnected — rather than fading over weeks — the cause is more likely the pairing or a stored fault than the coin cell; you can look up what a logged code means on autodtcs.com.
Independent guide — not affiliated with Peugeot. Always follow your official service manual and safety precautions. Read our full disclaimer.