These instructions apply to the Vauxhall Astra Mk8 (L) 2022-Present.
For other models, please choose your vehicle here.
If the remote on your Vauxhall Astra Mk8 (Astra L, 2022–present) has to be almost touching the door before it responds, or it has stopped working while the car still starts once the fob is held to the button, the coin cell inside is nearly always the culprit. This generation moved onto Stellantis’ eVMP platform, so the Astra L no longer uses the old GM-style flip key — it carries a PSA/Stellantis key shared with cars like the Corsa F and Peugeot 308. Depending on trim you have either a standard remote or the keyless “Open & Start” smart key, but both hide a pull-out emergency blade and both open the same way. Here is exactly how to swap the cell, how to spot a dying battery, and why cutting a brand-new key is still a dealer job.
How to Tell the Fob Battery Is Dying
- Shrinking range. You have to stand right next to the Astra — or press the fob against the door handle — before it locks or unlocks. This is the first and most reliable warning.
- Keyless entry stops sensing you. On Open & Start cars, the door handles no longer unlock as you grip them, and the car won’t recognise the fob to start until you hold it to the marked spot.
- A “key battery low” message. The Astra L’s driver display shows a low key-battery warning when the smart fob is weak — don’t ignore it, because a fully flat fob makes keyless entry fail.
- Intermittent buttons in the cold. A near-flat lithium cell struggles at low temperature, so a fob that’s fine at midday can drop out on a frosty morning.
A CR2032 in an Astra fob typically lasts two to four years. If yours is around that age and doing any of the above, fit a fresh cell before you start suspecting the car’s receiver or immobiliser.
The Battery You Need
Both the standard remote and the keyless smart key take a single CR2032 — a 3-volt, 20 mm lithium coin cell, the most common fob battery there is and stocked by any supermarket or hardware shop. Buy a good-quality branded cell: cheap coin cells sag under the brief high current the transmitter draws and can give poor range even when they read as “new”. Before you order, it’s always worth opening the fob and checking the code printed on the cell you remove — on this platform it is CR2032, but matching the marking removes all doubt.
Method 1 — Standard Remote and Keyless Smart Key
The Astra L’s two fob types open identically, so this one procedure covers both.
- Release the emergency blade. Slide the small catch on the fob and pull the mechanical key blade straight out of the body. This exposes the seam you need.
- Split the case. Insert a small flat-bladed screwdriver (or a plastic pry tool) into the slot the blade leaves behind and gently twist to part the two halves. It can feel tight the first time — work slowly rather than forcing it, so you don’t snap the internal clips.
- Note the orientation, then lift out the old cell. On this Stellantis key the CR2032 normally seats with the positive (+) face upward, but always copy the way the cell you removed was sitting rather than assuming.
- Fit the fresh CR2032. Press it home under its clip so it sits flat against clean contacts, positive side matching what you noted.
- Reassemble. Click the two halves back together around the edge until they seat evenly, then slide the emergency blade back in until it latches.
⚠️ Get the polarity right. A coin cell fitted upside down won’t power the fob and can slowly discharge against the contacts — so match the orientation of the old cell and make sure the case closes flush, with nothing trapping the battery proud of its seat.
Confirm It Worked
Stand back a few metres and lock, then unlock, the Astra. Full range should return straight away. On an Open & Start car, walk up and try the handles — keyless unlocking should sense the fob again — then confirm the car reads the key at the start button. Any “key battery low” message usually clears once the car has read a healthy fob, occasionally after one drive cycle rather than instantly.
If a Fresh Cell Doesn’t Fix It
- Re-check polarity and seating. The single most common mistake is an upside-down or loosely seated cell — it must click firmly under its clip against clean metal contacts.
- Wipe the contacts. A smear of finger grease or a little corrosion on the terminals is enough to cause dropouts; clean them with a dry cloth before refitting.
- Try the spare. If the second key works normally with a good battery, the first fob’s transmitter may have failed — rare, but it happens.
- Rule out the car. A weak 12 V vehicle battery can make the whole car slow to wake and mimic a key fault. If the Astra itself is sluggish to respond, the starting battery — not the fob — may be the real issue.
New Key or Spare — Why It’s a Dealer Job
Swapping the coin cell keeps the fob’s existing coding, so nothing needs reprogramming and the key works the moment the case is back together. A new key is a different matter: on the Stellantis platform the blade has to be cut to the car and a blank fob has to be coded to the immobiliser with a diagnostic tool, ordered against the Astra’s VIN. That makes adding a spare or replacing a lost key a job for a Vauxhall dealer or an auto-locksmith — so keep the battery in your spare fresh too, and you’re never down to a single working key.
Frequently Asked Questions
What battery does a Vauxhall Astra Mk8 key take?
A single CR2032 3-volt lithium coin cell — the same cell for both the standard remote and the keyless Open & Start smart key. Check the marking on the old cell before buying to be certain.
How do I open the Astra L smart key?
Pull out the emergency blade first, then insert a small flat screwdriver into the slot it leaves and gently twist to split the two halves. There’s no hidden screw — it’s a pry-apart case.
Which way up does the battery go?
Positive (+) side up is the norm on this Stellantis key, but always match the orientation of the cell you removed. Fitting it the wrong way round leaves the fob dead and can slowly flatten the new cell.
Do I need to reprogram the key after changing the battery?
No. A battery swap doesn’t touch the fob’s coding, so it works immediately. Only a brand-new key needs programming to the car.
How long should an Astra Mk8 key battery last?
Typically two to four years. Leaving a keyless fob sitting close to the car so it wakes constantly, or heavy remote use, shortens that.
Can I still drive if the fob 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 near the start button — the keyless system is designed to still start the car from a flat fob battery, so a dead cell won’t strand you.
If your remote died suddenly right after the 12 V battery was disconnected — rather than fading gradually — the cause is more likely a pairing or stored fault than the coin cell; you can look up any logged code on autodtcs.com.
Independent guide — not affiliated with Vauxhall. Always follow your official service manual and safety precautions. Read our full disclaimer.