Replace the Key Fob Battery

Last updated: June 5, 2026

If the remote or keyless fob on your Ford Focus Mk4 (2019–present) only works from up close, or has stopped locking the car, the fob’s coin battery is almost always the cause — and it is a quick change. This guide shows how to swap the key fob battery and what needs a dealer.

First, Rule Out the Battery

A weak fob battery is the number-one reason a Focus remote becomes unreliable — short range, needing several presses, or keyless entry/start failing. Most Focus Mk4 fobs use a CR2032 coin cell.

Replacing the Fob Battery

The Focus came with two fob styles — watch the polarity, as it differs between them:

1. Type 1 (flip/remote key): insert a small screwdriver and separate the two halves of the case. Remove the old CR2032 and fit the new one positive (+) side up. Clip the case back.
2. Type 2 (keyless fob): press and hold the buttons, pull out the metal key blade, remove the key cover and pull out the cell cover. Fit the new CR2032 positive (+) side down, then refit the blade and cover.

After a battery change the fob keeps its programming — no re-pairing needed.

Lost Key or Adding a Spare

The Focus Mk4 cannot have a key programmed without a diagnostic tool. A lost or extra key must be ordered and coded by a Ford 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 polarity — it is positive-up on the flip key but positive-down on the keyless fob, so confirm which you have.
• Use the metal key blade (hidden in the fob) to unlock the door, and hold the fob against the start button to start if its battery is flat.
• 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 Focus Mk4 key take?

A CR2032 coin cell. Note the polarity differs by fob type — positive up on the flip key, positive down on the keyless fob.

Do I need to reprogram after changing the battery?

No — programming is retained. Just fit the CR2032 the correct way round for your fob type and test.

Can I program a new Focus key myself?

No — the Focus Mk4 needs a diagnostic tool to register a key, so a new or replacement key must be coded by a Ford dealer or locksmith.

How do I start the car if the fob is dead?

Use the hidden metal key blade to unlock, then hold the fob against the start button and press — the car reads the transponder directly.

If the remote stopped working after a battery disconnection, see our Ford Focus Mk4 battery disconnect/reconnect guide.