These instructions apply to the Vauxhall Astra Mk7 (K/B16) 2015-2021.
For other models, please choose your vehicle here.
If the remote for your Vauxhall Astra K (2015–2021) — sold as the Opel Astra K across the rest of Europe — only locks the car from a pace or two away, has started missing button presses, or has stopped working altogether, the coin cell inside it is almost certainly flat. Nearly every Astra K left the factory with GM’s familiar folding “flip” remote, where the metal blade swings out of the fob body at the press of a button. Higher trims fitted with Keyless Open & Start (passive entry) instead carry a fixed-shape smart fob with a hidden emergency blade. Both take the same battery but open in different ways, so this guide covers each — plus how to be sure it’s the cell and not the car, and why cutting a brand-new key is the one job you can’t finish at home.
How to Tell the Fob Battery Is Dying
- Shrinking range. You find yourself standing right next to the Astra — or holding the fob against the door handle — before it will lock or unlock. This gradual loss of range is the classic first warning.
- The button LED goes dim or dark. The little indicator on the remote should flash brightly on each press; if it’s faint or dead with the buttons working only occasionally, the cell voltage has dropped.
- A key-battery warning in the cluster. Keyless Open & Start cars display a low-key-battery message on the driver information centre when the smart fob is weak; a plain flip-key car has no such warning, so you rely on the range and LED symptoms.
- Cold-weather dropouts. A cell that’s almost flat sags further in the cold, so intermittent response on frosty mornings that recovers by afternoon points squarely at the battery.
A CR2032 in an Astra K remote usually lasts two to four years. If yours is around that age and showing any of the above, fit a fresh cell before you start suspecting the receiver or immobiliser.
The Battery You Need
Both the folding flip remote and the Keyless Open & Start smart fob use a single CR2032 — a 20 mm, 3-volt lithium coin cell, and the most common fob battery there is. You’ll find it in any supermarket, hardware shop or petrol station. Buy a good-quality branded cell: cheap unbranded coins sag under the brief high current the transmitter draws and are the single biggest cause of “new battery, still poor range” complaints on the Astra.
Method 1 — Folding “Flip” Remote
- Press the release button so the metal blade springs out, then fold it closed again — swinging it out first frees the two case halves and gives you something solid to hold.
- Turn the fob over so the buttons face down and find the small slot in the seam on the back, next to the silver split-ring loop.
- Rest a small flat-blade screwdriver in that slot against the key loop and gently lever the plastic back cover away from the body. It can feel tight the first time — work along the seam rather than forcing one spot.
- Separate the halves to expose the coin cell. Note which way up it sits, ease it out, and drop the fresh CR2032 in the same orientation — copy the cell you removed rather than assuming.
- Press the two halves back together until they click all round, then test every button and the fold-out blade.
Method 2 — Keyless Open & Start Smart Fob
- Release the emergency blade first: slide the catch on the fob and pull the mechanical key blade straight out. This uncovers the slot the case splits along.
- Insert a flat plastic tool (or the emergency blade itself) into that seam and gently twist to part the two halves of the case — go slowly to avoid marking the shell.
- Lift out the old CR2032, noting its orientation, and seat the new one exactly the same way round.
- Click the halves back together and slide the emergency blade home until it latches.
⚠️ Match the polarity. A coin cell fitted the wrong way round won’t power the transmitter and can slowly discharge against the contacts, so always mirror the orientation of the cell you took out. If you didn’t note it, the printed “CR2032” face is the positive (+) side.
Confirm It Worked
Stand back a few metres and lock, then unlock, the car. Full range should return straight away and the LED should flash brightly again. On a Keyless Open & Start Astra the low-key-battery message clears once the car next reads a healthy fob — sometimes instantly, sometimes after a short drive cycle. If passive entry still won’t wake the door handles, carry the fob right up to the handle once to let the car re-detect it.
If a Fresh Cell Doesn’t Fix It
- Re-check seating and polarity. The cell must sit flat under its clip with the correct face up; a coin that’s slightly proud or upside-down is the most common reason a “new” battery does nothing.
- Clean the contacts. A smear of finger grease or light corrosion on the terminals is enough to cause dropouts — wipe them with a dry cloth before refitting.
- Try a different branded cell. A weak or counterfeit CR2032 can read as “new” yet fail to drive the transmitter; swap in a fresh branded one to rule it out.
- Suspect the car’s own 12 V battery. A tired vehicle battery can make the Astra slow to respond and mimic a key fault. If the car itself is sluggish to wake, that’s worth checking separately from the fob.
New Key or Spare — Why It’s a Dealer Job
Changing the coin cell leaves the fob’s existing coding untouched, so the remote keeps working with no reprogramming needed. A new key is a different matter: the Astra K’s immobiliser has to be accessed with GM-compatible diagnostic equipment, blank keys must be cut to the car and coded against its security data, and a Keyless Open & Start fob has to be paired to the passive-entry system. That puts adding a spare or replacing a lost key firmly with a Vauxhall/Opel dealer or a qualified auto-locksmith — so keep the battery in your spare fresh too, and you’ll never be down to a single working key.
Frequently Asked Questions
What battery does a Vauxhall Astra K key fob take?
A single CR2032 3-volt lithium coin cell. It’s the same cell whether you have the folding flip remote or the Keyless Open & Start smart fob.
How do I open the Astra K flip key?
Turn it buttons-down, rest a small flat screwdriver in the slot on the back beside the key ring, and lever the plastic cover off to split the case. Swinging the fold-out blade open first makes the halves easier to part.
Which way round does the battery go?
Fit the new cell the same way up as the one you removed. If you didn’t note it, the face stamped “CR2032” is the positive (+) side — getting it the wrong way round stops the fob working.
Do I need to reprogram the key after changing the battery?
No. A battery swap doesn’t affect the coding, so the remote works as soon as the case is back together. Only cutting or coding a brand-new key needs dealer programming.
How long should an Astra K key battery last?
Typically two to four years. Heavy remote use, or leaving a Keyless fob sitting near the car so it wakes constantly, shortens that.
Can I still drive the Astra if the fob battery is completely dead?
Yes. Use the emergency blade inside the fob to unlock the driver’s door. On Keyless Open & Start cars, hold the fob against the start button (or in the designated spot) so the car can read it directly, and it will still start with a flat cell.
If your remote died suddenly right after the car’s 12 V battery was disconnected — rather than fading over weeks — the pairing, not the cell, is the more likely cause, and the Astra may have logged a related fault; you can look up any stored code on autodtcs.com.
Independent guide — not affiliated with Vauxhall. Always follow your official service manual and safety precautions. Read our full disclaimer.