These instructions apply to the BMW 1 Series Mk2 (F20/F21) 2011-2019. For other models, please choose your vehicle here.
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If the remote on your BMW 1 Series (F20/F21, 2011–2019) only works from up close, or has stopped locking the car, the fob’s coin battery is almost always the cause — and on the standard (non-rechargeable) key it is a quick change. This guide covers swapping the fob battery and explains the difference between the standard key and the Comfort Access key.
Standard Key vs. Comfort Access Key
The F20 came with two key types:
- The standard remote key uses a replaceable CR2450 coin cell — the job below.
- The Comfort Access (keyless) key has a rechargeable cell that tops up when the key is near/inserted in the slot — it is not a quick coin-cell swap, and a failing one usually needs a dealer/specialist.
If your key has no slide-out section for a coin cell, you likely have the rechargeable Comfort Access type.
Replacing the Standard Fob Battery
- Press the release and pull out the mechanical (emergency) key blade — this releases the cover.
- Remove the key cover at the seam revealed by the blade slot.
- Lift out the old CR2450 cell.
- Fit the new cell with the positive (+) side facing upwards.
- Refit the cover and slide the blade back in. Test the remote.
After a battery change the remote keeps its programming — no re-pairing needed.
Lost Key or Adding a Spare
The F20 cannot have a key programmed without a diagnostic tool. A lost or extra key must be ordered and coded by a BMW dealer or an auto-locksmith with the right equipment — there is no owner sequence. The home job is limited to renewing the battery in a key that already works.
If a Fresh Battery Doesn’t Fix It
- Check the cell type and polarity — a CR2450 fitted the wrong way gives no response.
- Use the mechanical blade (hidden in the fob) to unlock the door, and hold the fob against the start button to start if the battery is flat.
- Comfort Access key going flat quickly? The rechargeable cell may be worn — that typically needs a specialist.
- Still nothing from any key? A receiver or body fault may be involved — check the code on autodtcs.com.
Frequently Asked Questions
What battery does the F20 key take?
The standard remote key uses a CR2450 coin cell. The Comfort Access key uses a rechargeable cell that is not a simple swap.
Do I need to reprogram after changing the battery?
No — programming is retained. Just fit the CR2450 the right way round and test.
Can I program a new BMW key myself?
No — the F20 needs a diagnostic tool to register a key, so a new or replacement key must be coded by a dealer or locksmith.
How do I start the car if the fob is dead?
Unlock with the hidden mechanical blade, then hold the fob against the start/stop button and press — the car reads the transponder directly.
If the remote stopped working after a battery disconnection, see our BMW 1 Series F20 battery disconnect/reconnect guide.
Disclaimer: The information on this page is provided for general guidance only. Always follow your official service manual and safety precautions when working on your vehicle. We are not responsible for errors, omissions, or any damage resulting from the use of this information.
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