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Mazda MX-5 Miata Key Fob Battery Replacement Guide
How to change a dead battery in the advanced key fob for a fourth generation 2016 to 2021 Mazda MX-5 Miata.

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2018 MX-5 Miata Fob
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Back Side of Key Fob
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Small Release Switch
This automotive maintenance tutorial was specifically written to assist owners of the 4th generation (2016, 2017, 2018, 2019, 2020 & 2021) Mazda MX-5 Miata in changing the battery in the "smart" or "intelligent" key fob remote control for the Advanced Keyless Entry system.

Owners of other Mazda vehicles such as the Mazda2 (Demio), Mazda3 (Axela), Mazda5, Mazda6 (Atenza), CX-3, CX-5, CX-7, CX-9, RX-8 and MPV may also find these DIY instructions to be helpful.

The compatible replacement coin cell (also known as a "button" or "watch") battery is part number CR2025 which is available from various manufacturers such as Panasonic, Duracell, Energizer, GE and Maxell.

The only tool needed to access and replace the battery is a small flathead screwdriver or a plastic pry bar tool.



 

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Slide Release Switch
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Pull Out Metal Ignition Key
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Backup / Emergency Key
The first step is to turn over the key fob.

Locate the small switch on the back side of the fob.

Slide the switch to release the metal emergency / backup ignition key.

Pull the key out of the slot and set it aside in a safe place.

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Pry Apart Two Halves
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Rear Cover Removed
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Round Battery Cover
Insert a small flathead screwdriver or a small plastic pry bar tool in between the two halves of the fob.

To prevent from scratching the plastic surfaces, you can either cover the screwdriver with a thin micro fiber cloth or use the plastic automotive trim panel removal tool.

Try to avoid using excessive force. The two halves of the fob should pop apart relatively easily.

Continue separating the back cover from the fob housing at every edge to release the plastic retaining clips.

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Pry Off Battery Cap
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Battery Cover Removed
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Tap Out Old Battery
Set the rear cover aside in a safe place.

Gently pull off the round black plastic cap that covers the battery socket.

Use your fingernail or the screwdriver to pry out the old battery from the holder.

I just turned the fob over and tapped it on the counter to pop it out of the socket.



 

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Old Battery Removed
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Empty Battery Socket
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Install New Battery
The original OEM battery in this 2018 MX-5 Miata was a Panasonic CR2025 3 volt coin cell.

Orientate the new battery with the positive "+" side facing up towards you and the negative "-" side facing down into the socket.

Push the new CR2025 battery into the socket.

Make sure it is fully seated and securely in place.

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New Battery In Holder
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Line Up Battery Cover
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Pop On Battery Cover
Line up the round black plastic battery cap.

Push the battery cover into place.

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Line Up Back Cover
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Snap Together Two Halves
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Slide In Metal Ignition Key
Line up the rear cover with the fob assembly.

Gently pop the rear cover into place.

Make sure that the two halves of the fob are flush together at every edge.

Slide the emergency / backup metal ignition key into its slot.

The key should "click" securely into place.

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Key Fob Re-Assembled
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Stand Near Miata
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Test Key Fob Battery
To test the new battery, stand near your Miata and press the "Unlock" or "Lock" buttons.

If the new battery is working properly and was installed in the correct orientation, you should see the parking lights and headlights flash and also hear the door locks opening or closing.

The fob should not need to be re-programmed. Just changing the battery should not clear the original programming.

Be sure to record the battery change in your vehicle's service records.

For more, check out all of my 2016-2021 Mazda MX-5 Miata DIY Repair & Maintenance Guides.
 

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