These instructions apply to the MG MG3 Mk1 (SZP1) 2011-2023.
For other models, please choose your vehicle here.
If the remote for your MG MG3 (2011–2023) only locks the car from arm’s length, works one press in three, or has stopped doing anything at all, the coin cell inside it is almost certainly flat. Across its whole run the MG3 — SAIC’s budget supermini, sold in the UK and Europe as a simple, well-equipped city car — used a single folding “flip” remote key rather than a keyless smart fob: the metal blade swings out of the plastic body, and the transmitter and its battery live in the same case. That keeps this an easy driveway job. Below is exactly which cell it takes, how to crack the case open without snapping anything, and why a brand-new key is the one part of this you can’t finish yourself.
How to Tell the Fob Battery Is Dying
- Shrinking range. You have to be right next to the MG3 — sometimes almost touching the door — before it will lock or unlock. This is the first and most reliable warning.
- Hit-and-miss buttons. The remote responds to one press and ignores the next, or needs two or three jabs to react. A weak cell can’t sustain the brief burst of current the transmitter needs.
- The immobiliser light flashes. MG’s own handbook notes that when the remote battery is low, the engine-immobiliser warning lamp in the instrument pack flashes when you operate the key (or with the ignition on) — a deliberate cue to change the cell.
- Cold-morning dropouts. A cell that is fine on a mild afternoon but dead first thing on a frosty morning is on its way out — low temperature drops its voltage below the fob’s threshold.
A coin cell in an MG3 remote typically lasts two to four years. If yours is around that age and showing any of the above, fit a fresh battery before you start suspecting the car’s receiver or the immobiliser.
The Battery You Need
The MG3 flip remote takes a single CR2032 3-volt lithium coin cell — the most common fob battery there is, sold in any supermarket, hardware shop or petrol station. It is a standard 20 mm size, cheap and easy to find. Buy a fresh, good-quality cell: coin cells that have sat on a shelf for years, or very cheap unbranded ones, can sag under the transmitter’s current draw and give poor range even when “new”. If the cell you lift out is marked with a different code (some remote variants use a CR2025 of the same diameter), simply match whatever is printed on the old battery.
How to Change the MG3 Remote Battery
- Swing the metal blade out. Press the release and let the folding key blade flip open — it gives you something firm to hold and exposes the key groove where the cover comes off.
- Prise off the small cap. Look in the key groove for the two small square holes. Slip the tip of a small flat-bladed screwdriver into them and gently lever the cover off the back of the fob. Work slowly — the housing is plastic and the tabs are fine.
- Lift out the waterproof gasket. MG3 remotes have a thin rubber seal under the cover. Set it aside carefully; it has to go back or the fob loses its splash resistance.
- Note the orientation, then remove the old cell. Look at which face of the battery points up, then press it to one side and ease it out from under its retaining clip with a fingernail or the screwdriver tip.
- Fit the new CR2032 the same way round. Seat the fresh cell in the exact orientation the old one came out — on most MG3 remotes the positive (+) face sits downward, against the base of the holder, but always copy what you removed rather than trusting a rule of thumb.
- Refit the gasket and cover. Lay the seal back in place, line up the cap and press it home until the tabs click. Fold the blade away and test every button.
⚠️ Get the polarity right. A coin cell fitted upside down makes no contact — or worse, can slowly discharge itself — so the single most useful thing you can do is photograph or simply remember which way the old cell faced before it leaves the holder.
Make Sure It Took
Stand back a few metres and lock, then unlock, the MG3. Full range should return straight away. If the immobiliser warning lamp had been flashing when you pressed the key, it should stop once the fob is transmitting normally again. If range is still short, open the case back up and confirm the cell is seated flat under its clip and the right way up before looking any further.
If a Fresh Cell Doesn’t Fix It
- Re-check polarity and seating. An upside-down or loosely-clipped cell is by far the most common reason a “new” battery doesn’t help. The battery must sit flat against clean contacts.
- Clean the contacts. A smear of finger grease, or light corrosion on the terminals or the cell face, is enough to cause dropouts. Wipe both with a dry, lint-free cloth.
- Try the other button first. If lock works but unlock doesn’t (or vice versa) with a known-good cell, the fault is more likely a worn micro-switch in that button than the battery.
- Rule out the car. Rarely, a weak 12 V starter battery can make an MG3 slow to respond to the remote and mimic a key fault. If the car itself is sluggish to wake, the vehicle battery — not the fob cell — may be the real culprit.
New Key or Spare — Why It’s a Dealer Job
Changing the coin cell does not touch the fob’s coding, so the remote keeps working immediately with no reprogramming. A new key is a different story. MG’s handbook is explicit that a replacement key can only be obtained through an MG Authorised Repairer, and warns that a key made outside that network may not start the engine and could compromise the car’s security — because the blade has to be cut to the car and the transponder married to the MG3’s immobiliser with diagnostic equipment. In practice, a spare or a lost-key replacement means an MG dealer or a qualified auto-locksmith — so keep the battery in your spare fresh too, and never let yourself get down to a single working remote.
Frequently Asked Questions
What battery does an MG3 key fob take?
A single CR2032 3-volt lithium coin cell. It is a standard 20 mm size stocked almost everywhere. If the cell you remove happens to carry a different code, match that instead.
Which way round does the battery go?
Fit the new cell in the same orientation as the one you took out. On most MG3 remotes the positive (+) face points downward into the holder, but the safest approach is always to copy the old cell rather than rely on a general rule.
Do I have to reprogram the MG3 key after changing the battery?
No. Swapping the coin cell leaves the fob’s coding untouched, so it works the moment the case clicks back together. Only a completely new key needs programming.
How do I open an MG3 flip key without breaking it?
Fold the metal blade out, then prise the small cover off the back using the two square holes in the key groove with a fine flat screwdriver. Lift out the rubber waterproof seal, and the battery is underneath. Take it slowly — the plastic tabs are thin.
How long should an MG3 key battery last?
Usually two to four years. Heavy daily use of the remote, or a fob that gets knocked about in a pocket or bag, tends to shorten that.
Can I still drive the MG3 if the fob battery is completely dead?
Yes. Use the folding metal blade in the key to unlock the driver’s door manually, then start the car with the key in the ignition as normal — a dead remote cell won’t strand you.
If your MG3’s remote stopped working suddenly and the immobiliser light keeps flashing even with a known-good battery, it is worth reading any fault code the car has stored before assuming the key is the problem — you can look up what a logged immobiliser or body-control code means on autodtcs.com.
Independent guide — not affiliated with MG. Always follow your official service manual and safety precautions. Read our full disclaimer.