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How to: Change your mk3 key fob battery
Contents

Please read this guide in its entirety before picking up any spanners. Skipping ahead or rushing could
cause you problems further down the line.

This car in this guide is a 2005-2008 mk3 and maybe 3.5.​

When does it need doing?
When your battery goes. Your buttons will start needing a second press or just suddenly stop working one day.

What do I need?
Small electrical screw driver.
A lithium battery - CR1620 type.

How do I do it?
I should add I got this information from URN who found this on
http://mx5life.com/community/threads/mk3-keyfob-battery-replacement.25/

1) Flip the key open so it looks like it is ready to go in the ignition.
ADC7B2C0-DE0E-4B84-8AD1-69FC28ED6042-502


2) Inside the key recess there is a tiny little notch. Press inside this notch with your screw driver. This will release the top from the bottom.
FACDD1BF-8EAF-4AFF-8309-B2762630A57C-502

This will leave you with this
165D62CC-FC20-41EE-8627-E6806810DC18-502


3) Next you will see a small rectangle indent at the top of the larger section. Again you need to press this and push it as hard as you feel.
This will split the key in half.
E7FD3EBD-BD00-4EFC-B3FC-9F37530277DE-502


4) Now you will see the battery on one half of the key. Replace with CR1620 lithium battery. Be careful not to touch these batteries with greasy fingers.
2198F471-F436-41A7-8D85-27B18B123153-502


5) Ensure it is the right way and literally clip everything back together. It all goes on the same way as it got taken to bits.

6) Test out your key to make sure the red LED flashes.

As I have previously said I have just regurgitated information found from http://mx5life.com/community/threads/mk3-keyfob-battery-replacement.25/
linked to me by URN in a PM.

I have taken my own pictures and wrote it up on here in my own words for mx5nutzers to access. Saves a massive dealer bill... around 80 quid.

Battery cost me around 4 pounds from a watch specialist. Maybe more or maybe less depending on where you get it from.
 

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Good write up Jon.

£80 from the main stealer........that's a complete joke!!

Thought I got ripped off paying £17 to have the receptionist change my battery at the local Nissan dealer a few years ago for one of my previous cars........this was before I had discovered owners clubs on the net.

Regarding the MK3 I got two new batteries for £2.50 from e-bay, from a seller in Hellaby last year.

Job done, at a fraction of the price charged by Mazda so it seems!
 

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Excellent write-up Jon.

There's also a Service Bulletin (see link below) for Mazda dealers about a known fault with the connections in the key. It's to do with making the little spring 'terminals' underneath the battery 'bend up' at the right angle for a good contact..

I mended both my keys this way, with new batteries, using the service bulletin tips, when one became a bit 'intermittent' a week after buying the car. Use top quality Panasonic Lithium batteries, like the originals, they last for years. I bought these: Four genuine batteries for £3.79 http://www.ebay.co.u...K-/320761747882

http://www.miata.net...b/09-003-10.pdf
 

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That's very interesting about the Service Bulletin Robin, seems to be the likely cause why my partners son was having so much trouble with his key fob, even after installing new batteries.

Bargain on the batteries too!
 

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Yes it sorted mine without a repeat of the problem, it's now 4 months on..

You have to be very careful not to snap the terminals by bending them up, use a plastic tool or tape around a screwdriver as suggested, also clean the battery in a soft cloth and don't touch it with your bare fingers at all (we all have oils naturally on our fingertips, it's what fingerprints are made of) this will ensure a good contact.

The final pic in the bulletin shows you how much to bend the terminals up for a secure connection.


Mine is very intermittent robin, is it just a case of bending the contacts up? Ill have a look at the bulletin when I get home.
Have a look to see if the little red led light in-between the two main buttons lights up. If it does everytime (but weakly) then it's a dying battery, if your light is intermittent then it's likely to be the contact issue, it's been quite common in the States (which is where I found the Bulletin). New batteries and bent up terminals = problem gone.
 

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Discussion Starter · #7 ·
I thought it might have been something to do with the contacts as mine would occasionally be intermittent but I do think my battery did actually die. I have no bent the terminals up and all is working again. Do the terminals just flatten with age?
 
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