Key fob low battery on dash but new batteries?

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N. California
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2022 CX-5 SG
I use the thicker 2032 in my 2016.5 fob, which specifies the thinner 2025. Works fine, longer life.
That may be one of the reasons why Mazda went with the newer and fatter fob... I never got more than a year out of the 2025 batteries in the old key remotes but my newer ones have given me over two years with no problems.
IMG_1737.jpg
 

Gozo

2020 Mazda6 2.5T
Hopefully that’s just the perspective of the photo angle, that the new fob looks that much bigger than the old one. And I thought that the old one was way bigger than it needed to be. Soon it’s going to be like dragging a paperback romance novel along with you.
 
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N. California
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2022 CX-5 SG
Yes, it is the perspective. They are both the newer keys but the one in front is in a case.
 
I'll bet you left the key in the car or close enough to activate the power save feature. The same thing happened to my extra fob and this solved the issue. I swapped the battery to no avail then remembered seeing this somewhere in the manual.

Turning off the power saving function

After you have turned off the power saving function according to the following
procedure, the hazard warning lights and sound operate*1 one time.

1. Press any of the buttons on the transmitter to make sure that the operation indicator light does not turn on/flash.

2. Press the lock button on the transmitter 4 times within 3 seconds to turn on the operation indicator light.

3. Press the lock button continuously for1.5 seconds or longer while the
operation indicator light turns on (for 5seconds).
I tried this but it did not work, so I went to my Mazda dealer. For my 2020 CX5, one must push the lock button five times, I think. One of the people at the dealership pushed four and that did not fix the problem, but another person pushed five times and that did the trick.
 
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Ottawa, Ontario
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17 Mazda 6 GT
Had this problem the last month as well in my 2017 6.
Tried new batteries, as well as the thicker 2032, and nothing changed. All batteries showed over 3 volts on my volt meter and I still got the message.
Finally decided to swap batteries with my other fob (which rarely gets used) as a test, and now both of them are working fine. Go figure.
 

HardRightEdg

US 2020 CX-5 Touring AWD Soul Red
I got the low battery warning on one fob after 2.5 years from new. Didn't bother to check the other. Started the vehicle a couple of times before installing new batteries in both fobs. Didn't have to perform the 4-press operation--just "plug and play" the batteries and good to go. Go figure.
 

AVC

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'17 CX-5 Select
Note that these button cells batteries may test above 3.0v using a digital meter and fail in a FOB. The batteries MUST be tested under load; the better purpose-built battery testers do loaded measurements.

Also, heat and in some cases extreme cold (below 0F) can prematurely age the batteries.

Last, not uncommon for Amazon, shelf stock in stores and dealership stock to be aged and nearly flat (pun). For my last FOB battery change, I threw out an entire card of 8 button cells as they all failed loaded test. A batch of fresh Panasonics fixed the recurring poor FOB performance.
 
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2019 CX-5 Signature
Note that these button cells batteries may test above 3.0v using a digital meter and fail in a FOB. The batteries MUST be tested under load; the better purpose-built battery testers do loaded measurements.
...
I'm not sure what apparatus you're using to measure 3V DC coin cell batteries, but my Fluke multimeter with its 10 mOhm input impedance has no issue.
 

AVC

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'17 CX-5 Select
I assume you mean 10M ohm resistance, which is unloaded measurement. Exactly to my point. For example, a CR2032 test load is typically 190uA, or ~15k ohm.
 
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2019 CX-5 Signature
I assume you mean 10M ohm resistance, which is unloaded measurement. Exactly to my point. For example, a CR2032 test load is typically 190uA, or ~15k ohm.
Yes, 10 megaohm. We're measuring voltage, not current. My multimeter, used in the voltmeter setting, is correctly reading the battery's voltage.
 
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2016.5 CX-5 GT AWD titanium/black 2016 Miata Club ST MT white
I'm an EE, so thanks...

You're an EE who clearly doesn't understand that a battery needs a load on it to be properly tested.

10M ohm is NOT a load. To the battery it looks like an open circuit. Perhaps you missed that lesson in class? ;)

Yes, 10 megaohm. We're measuring voltage, not current. My multimeter, used in the voltmeter setting, is correctly reading the battery's voltage.

Yes, your DMM is correctly reading the voltage of the battery, but it is NOT testing the battery correctly.
 
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2019 CX-5 Signature
You're an EE who clearly doesn't understand that a battery needs a load on it to be properly tested.

10M ohm is NOT a load. To the battery it looks like an open circuit. Perhaps you missed that lesson in class? ;)



Yes, your DMM is correctly reading the voltage of the battery, but it is NOT testing the battery correctly.
As a working EE for over 30 years, I've learned to have a thick skin when it comes to things like this. If you and the other person truly believe a load test on a 3v DC coin battery is necessary to determine whether or not it's good, I really don't know what to tell you. :)
 
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Reactions: AVC
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2014 CX-5 Touring
Does any of this apply to 2014 models and fobs? My wife's key fob was recently showing the red key light on the dash, and she had to hold the fob to the start button to start the car. I changed the battery with a fresh one, and later she reported it still doing the same thing. Red key light, car wouldn't start unless hold the fob to the button. I also noticed no flashing LED on the fob itself when pressing any of the buttons.

For now we have swapped fobs since I don't use mine very much. But there was one day where my fob battery went completely dead and I couldn't even unlock the car while at a store. Had to call my dad to get my wife's key fob and bring it to me, which was pretty annoying having to stand around outside the store for 30+ minutes.
 
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2019 CX-5 Signature
... there was one day where my fob battery went completely dead and I couldn't even unlock the car while at a store. Had to call my dad to get my wife's key fob and bring it to me, which was pretty annoying having to stand around outside the store for 30+ minutes.
Is something wrong with the key inside the fob? I've only used ours once, just to make sure it worked.