These instructions apply to the Subaru Forester Mk5 (SK) 2019-Present.
For other models, please choose your vehicle here.
A Subaru Forester (fifth generation, SK, 2019–present) that will only lock or unlock with the fob almost touching the door, or that shows “Access key battery low” in the cluster, has a flat coin cell in the remote — not a fault in the car itself. This SK-generation Forester, including the e-Boxer mild hybrid, comes with Subaru’s Keyless Access smart fob and push-button start on most versions: the black remote carrying lock, unlock and tailgate buttons plus a slide-out mechanical blade. Changing the cell is a couple of minutes’ work with a small screwdriver. What follows is the exact battery, the trick to opening the case cleanly, and why a truly new key still needs a dealer’s kit.
How to Tell the Fob Battery Is Dying
- Range falls away. The remote that used to work from across the car park now needs you right at the door — the first thing owners notice.
- “Access key battery low” warning. The Forester displays this message in the instrument cluster as the smart fob’s cell fades; take it as your cue to change it.
- Push-button start hesitates. If the engine only starts with the fob held against the button, the transmitter is running low.
- Cold mornings expose it. A weak lithium cell loses voltage in the cold, so the fob turns unreliable when it’s freezing and improves as the day warms.
A Keyless Access cell usually lasts two to four years. If yours is around that age and behaving like this, renew the battery before you start suspecting the receiver or the immobiliser.
The Battery You Need
The Forester’s Keyless Access fob takes a single CR2032 3-volt lithium coin cell — the common 20 mm coin battery stocked in supermarkets, hardware shops and petrol stations. Glance at the code printed on the cell you remove to confirm, but on this generation it’s a CR2032. Choose a quality branded battery: budget cells sag under the brief burst of current the transmitter draws and can leave you with poor range even when the cell is new.
How to Change the Battery
- Slide out the auxiliary key. Press the release catch on the back of the fob and pull the metal emergency blade straight out.
- Open the case. Insert a small flat-blade screwdriver — tape the tip to protect the finish — into the slot the blade vacated, or the seam around the fob, and twist gently to separate the two halves.
- Reach the cell. Lift the back off to reveal the circuit board and the coin cell secured beneath a small clip.
- Note it, then swap. See which way the old CR2032 is facing before you work it out from under the clip, then push the fresh cell in the same orientation, holding it by the edge only.
- Close it up. Press the halves together until they click evenly all round, then slide the emergency blade back until it latches.
⚠️ Keep the polarity the same as before. Guides for Subaru smart keys disagree over whether the positive face points up or down, so don’t rely on memory — match the way the cell you removed was sitting. A reversed battery won’t drive the transmitter and can slowly discharge against the contacts.
Check It Worked
Move back a few metres and lock, then unlock, the Forester. Full range should come straight back, and the push-button start should sense the fob normally. The “Access key battery low” message clears once the car next reads a healthy fob — sometimes at once, sometimes after a short drive.
If a Fresh Cell Doesn’t Fix It
- Recheck the cell and its way up. Confirm it’s a CR2032, sitting firmly under the clip and facing the same direction as the original.
- Clean the contacts. Corrosion or finger grease on the terminals is a frequent cause of dropouts — wipe them with a dry cloth.
- Try the emergency start. Hold the fob against the start button while you press it; if the car starts, the transponder is fine and the problem is the battery or fob electronics, not the vehicle.
- Have the 12 V battery checked. On the e-Boxer especially, a tired 12 V battery can make the smart system slow and imitate a fob fault; get it tested if the Forester is generally slow to wake.
New Key or Spare — Why It’s a Dealer Job
A battery change keeps the fob’s existing coding, so nothing needs reprogramming and the remote works at once. A replacement or additional Keyless Access fob is a bigger job: Subaru’s immobiliser has to be accessed with diagnostic equipment to register the new key, blanks are ordered against the car’s VIN, and the emergency blade must be cut to the locks. That keeps adding a spare or replacing a lost key with a Subaru dealer or a reputable auto-locksmith. Keep the battery in your spare fob fresh as well, and a single dead cell can never leave you stranded.
Frequently Asked Questions
What battery does a 2019-onwards Subaru Forester key fob use?
The Keyless Access smart fob takes one CR2032 3-volt lithium coin cell. Check the code on the old cell to be certain before you buy.
Which orientation does the battery go in?
Guidance varies for Subaru smart keys, so the dependable method is to note how the existing cell sits and fit the new one exactly the same way.
Do I have to reprogram the fob after changing the battery?
No. Renewing the cell leaves the pairing intact, so the fob works immediately. Only a brand-new key needs programming.
How long should the fob battery last?
Roughly two to four years. Storing the fob close to the car, so it keeps waking the Keyless Access system, cuts that short.
My Forester fob still won’t work with a new battery — why?
Re-check the orientation and seating, then the contacts. If a known-good CR2032 still won’t work, the transmitter may have failed — unusual next to a flat or upside-down cell.
Can I drive the Forester if the fob battery is dead?
Yes. Unlock the door with the emergency blade, then hold the fob against the start button as you press it — the transponder still works, so a flat cell won’t strand you.
If the remote died the instant the 12 V battery was disconnected — rather than fading over time — the pairing is the more likely culprit than the coin cell; check any stored fault code first on autodtcs.com.
Independent guide — not affiliated with Subaru. Always follow your official service manual and safety precautions. Read our full disclaimer.