These instructions apply to the Mitsubishi Lancer Mk7 (CS) 2003-2008.
For other models, please choose your vehicle here.
If the remote on your Mitsubishi Lancer Mk7 (CS, 2003–2008) only locks the car from up close, needs a second or third press, or has stopped working altogether, the usual culprit is the small coin cell inside the key — not the car. It is a two-minute job with no tools beyond a small screwdriver. This guide shows how to open the Lancer key, which battery to buy, and how to check it worked.
How to Tell the Key Battery Is Weak
- Shrinking range. You have to be almost touching the car for it to lock or unlock, where it used to work from across the car park.
- Second- or third-press. The buttons work intermittently, and it is worse in cold weather when the cell sags under load.
- Nothing at all. A fully flat cell means no response — but you can still get into the car with the metal key (see below).
A coin cell in a remote like this typically lasts two to four years. If yours is older than that and doing any of the above, fit a fresh battery before suspecting the car.
The Battery You Need
The Lancer’s remote uses a single 3 V lithium coin cell. Rather than guess, open the key and read the code stamped on the cell you take out and match it exactly — remotes of this era typically use a CR1620 (in the flip-key type) or a CR2032 (in the larger separate fob). Buy a good-quality branded cell; cheap coin cells can read as flat almost from new.
How to Change the Battery
- Release the mechanical key if your remote is the flip-key type — slide the catch and fold or pull out the metal blade. On a separate fob, find the seam around the case.
- Split the case. Insert a small flat screwdriver (tape the tip) into the slot or seam and gently prise the two halves apart. Don’t force it — the clips are light.
- Note which way up the cell sits, then lift out the old coin cell. Handle the new one by its edge; finger grease on the faces can cause poor contact.
- Fit the new cell the same way round (usually positive + facing up, but copy what you removed) and press it under its clip.
- Clip the case back together and refit the mechanical key. Test lock and unlock from a normal distance.
Does It Need Reprogramming?
No. Replacing the coin cell does not affect the remote’s pairing with the car, so it keeps working the moment you reassemble it. Reprogramming is only needed for a brand-new or replacement key, which a Mitsubishi dealer or an auto-locksmith sets up against your car.
If a Fresh Cell Doesn’t Fix It
- Re-check the cell is the right way up and clipped down firmly — an upside-down or loose cell is the most common reason a “new” battery changes nothing.
- Wipe the contacts inside the key with a dry cloth to remove grease or corrosion.
- Confirm you fitted the correct cell code — a slightly thinner cell can sit loosely and give poor range.
- If it still will not work, the remote’s internals may have failed and need replacing, which is rare next to a simple flat cell.
Frequently Asked Questions
What battery does the Mitsubishi Lancer CS key take?
A single 3 V lithium coin cell. Read the code on the old one and match it — usually a CR1620 in the flip key or a CR2032 in the larger fob.
Do I need any tools?
Just a small flat-blade screwdriver to split the case, and clean dry hands. No programming equipment is needed for a battery swap.
Do I have to reprogram the key afterwards?
No. A battery change does not touch the coding, so the remote works as soon as you put it back together. Only a new key needs coding to the car.
Can I still get into the car if the remote is dead?
Yes. The metal key blade unlocks the driver’s door, and the car will still start normally — the flat coin cell only affects the remote locking, not the immobiliser.
How long should the key battery last?
Typically two to four years. If it is going flat much sooner, check you fitted a good-quality branded cell and that the contacts are clean.
My key still won’t work with a new battery — is the car broken?
Usually not. Re-check the cell orientation, seating and code, and clean the contacts. If it is still dead the remote itself is likely at fault, which a locksmith can renew — the car and its receiver are almost certainly fine.
If the remote stopped working suddenly — for example right after the car’s 12 V battery was disconnected — rather than fading gradually, it is worth reading any stored fault. You can look one up on autodtcs.com.
Independent guide — not affiliated with Mitsubishi. Always follow your official service manual and safety precautions. Read our full disclaimer.