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Discussion Starter #1
Hi,

I think my battery in my key fob is getting low and I keep losing signal to it so have to manually open car with aux key. Once this is done the key will work fine for awhile but if left over night, it doesn't work again until unlock with aux key.

I've tried replacing the battery but it doesn't work with the new batteries.

Even tried to unlock with aux key first but car doesn't detect the fob unless I put it right next to the start button (using the nfc)

Putting old battery in works fine but it'll stop working overnight and I have to do the unlock manually again before it works.

I do notice that the old battery has 2.8V while the new one is 3.2V. Is the keyfob really that sensitive to batteries? I'll try buying some brand name new ones and see what happen but in the meantime can anyone shed some light on this?

I've looked through google on "reprogramming" keyfob but it doesn't work and also I have a keyless start system so there is no key to start the ignition but following instructions doesn't work anyway as when the driver doors is open I can't "lock" key car with the lock switch on the door.

Any help would be appreciated else I may take it back to mazda for warranty or ask them how to do it.

Cheers
 

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The replacement battery should have the same voltage as the original. Assuming the battery in Australia is the same as North America, it's a CR2025, as per the manual. Check the manual for battery spec. My battery is original and 2 years old. Could be that the fob or replacement battery is faulty or it is the wrong one.
 

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New batteries are c. 3.0 - 3.2V then plateau at 2.8V for a long time after which the voltage drops off rapidly.Check your new battery is at least 3V, that the terminals are clean and that you insert the battery the right way around. Does the spare key work? If both keys with new batteries still cause problems then the issue may be with the car and not the key fob.
 

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Discussion Starter #4
Yeah the key when pressing the button lights up. Using a volt meter and measure the batteries as 3.2V so it's new. It's very annoying :( Putting old battery in again works but yeah it's running low.

I'll go to the shops tomorrow and buy another battery and see if that works else it'll be back to mazda.
 

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I've found that after I use the metal key or change a battery, the car doesn't recognize the fob until I press a button on the fob. That resets the communication between the fob and the car somehow.
If the car starts by holding the fob near the starter button, the system is communicating normally. The only purpose of the battery is to extend the range of the transmitter side of the fob. IOT seems like your fob is not transmitting a strong enough signal, but otherwise it is working OK. Does the other fob work normally?

Or maybe the system is refusing to work after you use the metal key or change the battery, and you just haven't understood that clearly.

Hope this helps.
 

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It's pretty clear it's the battery if the old one still randomly works which is what I recently experienced before I replaced mine...just go buy a new pack. I just replaced the battery in my key fob after 2 1/2 years and had to go thru 2 batteries in an already open pack before the last one worked. It seemed to be better sealed in the pack than the 2 batteries that didn't work.

One other consideration (and I'm not looking for a debate) is to use a 2032 if you have one laying around. The 32 is a bit thicker than the 25 and has a tad bit more battery life. The fob case will still seal and snap close, but just a little tighter.
 

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Discussion Starter #7
Ok bought from another new seal packed and battery works. So weird when the voltage are the same using multimeter to measure...........
 

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same thing happened to mine recently. just got energizer ones. cr2025 like some have said. works fine after..
 
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