Key fob low battery on dash but new batteries?

Is something wrong with the key inside the fob? I've only used ours once, just to make sure it worked.
I would bet there's a lot of people that don't even know there's a door key inside the FOB and what to do if the FOB doesn't open the door.
 
... 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.
If your 2014 is the same fob as my 2016.5, there should be a physical key that slides out the top (little release tab om the back of the fob) to unlock the door. Then just the fob (Mazda emblem down) against the start button.

Screenshot_20221025-115538.png
 
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. :)

I'm a retired EE with 30 years of experience in the field.

If you check a battery with a DMM and the measured voltage is below what the battery is rated for, then that battery is most likely in need of replacement or a charge, depending on the type of battery of course.

Checking a battery's voltage with a DMM can be an INDICATION of the battery's condition but not a true test.

What about a car battery? Does that need to have a load on it to test it properly? Of course, it does but just checking the voltage can give you an idea of what's going on.

You ever seen a simple battery tester that has a LED or other type of indicator that shows if a small battery is good or not? A small load is place on the battery for this test.
 
Last edited:
I'm a retired EE with 30 years of experience in the field.

If you check a battery with a DMM and the measured voltage is below what the battery is rated for, then that battery is most likely in need of replacement or a charge, depending on the type of battery of course.

Checking a battery's voltage with a DMM can be an INDICATION of the battery's condition but not a true test.

What about a car battery? Does that need to have a load on it to test it properly? Of course, it does but just checking the voltage can give you an idea of what's going on.

You ever seen a simple battery tester that has a LED or other type of indicator that shows if a small battery is good or not? A small load is place on the battery for this test.
I pointed out the fact that it's a simple 3V DC coin battery. A car battery is obviously a different story. For 99% of the people on this forum, a simple volt meter will suffice when measuring the fob battery. Then again, what's even the point when they're so cheap?
 
Is something wrong with the key inside the fob? I've only used ours once, just to make sure it worked.
forgot to mention, the fob remote is relatively new (car only came with one originally), programmed by Mazda a year or two ago, and it has a key blank inside it that I never got around to getting cut. So no, I didn't have the physical key available.
 
forgot to mention, the fob remote is relatively new (car only came with one originally), programmed by Mazda a year or two ago, and it has a key blank inside it that I never got around to getting cut. So no, I didn't have the physical key available.
Now you have a good reason to go get the blank cut. Not sure but probably a hardware store could do it since it just opens the door lock.
 
Now you have a good reason to go get the blank cut. Not sure but probably a hardware store could do it since it just opens the door lock.
yes I understand that, but my question was about the 13-16 key fobs and batteries, as my wife has been having trouble with hers. My issue is just plain ol' procrastination.
 
Now you have a good reason to go get the blank cut. Not sure but probably a hardware store could do it since it just opens the door lock.
Yes. I've had a couple of keys cut for mine from a local ACE store. Work fine to open the door.
 
yes I understand that, but my question was about the 13-16 key fobs and batteries, as my wife has been having trouble with hers. My issue is just plain ol' procrastination.
More than likely it the battery. Try buying one from a store that sells a lot of batteries and avoid the cheap ones from Amazon. They advertise they're Everyready but when you get them they're some cheap chinese crap. Also, buy a brand name.
I get my batteries from Harbor Freight and they seem to be fine.
 
yes I understand that, but my question was about the 13-16 key fobs and batteries, as my wife has been having trouble with hers. My issue is just plain ol' procrastination.
If you're asking if the replacement battery is good and you have no other way to test, just try swapping them between the 2 fob's. That should answer your question pretty quickly.
 
If you're asking if the replacement battery is good and you have no other way to test, just try swapping them between the 2 fob's. That should answer your question pretty quickly.
problem is that it seems to be an intermittent issue. This is on the original fob that came with the car, not the newer one we got recently. Sometimes the key light on the dash will show up red when pressing the brake pedal, and the car will refuse to start, but other times it will light up green and work fine.
 
problem is that it seems to be an intermittent issue. This is on the original fob that came with the car, not the newer one we got recently. Sometimes the key light on the dash will show up red when pressing the brake pedal, and the car will refuse to start, but other times it will light up green and work fine.
If I were you, I would take the battery out of that fob and inspect and clean the contacts. Also, look at the battery for any signs of debris. Not much more you can do if the battery is known to be good.
 
Have to comment about no load battery testing. Always test with a load for a true reading. This a fairly simple explainatio as to why.

Paul Menconi
E.E. in Electrical Engneering, University of California, Davis (Graduated 1971)Upvoted by
Kenneth Lundgren
, B.S. Electrical Engineering, Illinois Institute of Technology Chicago - Illinois Tech (1963)Author has 1.2K answers and 580.6K answer views2y
Open circuit voltage is the voltage of a voltage source (battery, power supply, whatever) with no load connected, with no current flowing. It will always be higher than any “closed circuit” voltage. (“Closed circuit voltage” isn’t really a thing; the correct phrase is “voltage under load”.)
The reason is internal resistance. Any real-world power source has some internal resistance In series with the output. As soon as you start pulling current from the source there is a voltage drop across that resistance, and the output voltage drops. The output voltage is effectively the difference between the open-circuit voltage and the drop across the internal resistance, which in turn depends on the current being drawn.
Now, while good power supplies have active feedback circuits that make that internal resistance look like zero, batteries do exhibit a lower voltage under load than when not loaded.
 
Have to comment about no load battery testing. Always test with a load for a true reading. This a fairly simple explainatio as to why.

Paul Menconi
E.E. in Electrical Engneering, University of California, Davis (Graduated 1971)Upvoted by
Kenneth Lundgren
, B.S. Electrical Engineering, Illinois Institute of Technology Chicago - Illinois Tech (1963)Author has 1.2K answers and 580.6K answer views2y
Open circuit voltage is the voltage of a voltage source (battery, power supply, whatever) with no load connected, with no current flowing. It will always be higher than any “closed circuit” voltage. (“Closed circuit voltage” isn’t really a thing; the correct phrase is “voltage under load”.)
The reason is internal resistance. Any real-world power source has some internal resistance In series with the output. As soon as you start pulling current from the source there is a voltage drop across that resistance, and the output voltage drops. The output voltage is effectively the difference between the open-circuit voltage and the drop across the internal resistance, which in turn depends on the current being drawn.
Now, while good power supplies have active feedback circuits that make that internal resistance look like zero, batteries do exhibit a lower voltage under load than when not loaded.
There are 2 types of engineers. The ones that use their education and experience and put it to use in a practical manner. And the ones that go to extremes and can't think outside of the box and say there's only one way to troubleshoot an issue. While it's not incorrect that load testing one of these 3V coin batteries can determine if it's god/bad, it's just not required for 99% of failures. When they die, they usually don't hold their voltage with any load.
 
No, just one of your large group of drooling, impractical dolting peers. Have to admit that in 40 years of career, you're the first engineer I've come across to argue himself into a corner re: diagnosing batteries--especially silver or lithium chemistry primary batteries--that without at least a moderate load wasn't begging for a misdiagnosis.

So I happen to have 3 CR2032 batteries from the card of 8 I tossed a few months ago. The terminal voltages with a 10M ohm DVM measured; 3.21, 3.25 and 3.27v. The battery tester I have applies a 2.5mA load for button cells, and has an LCD voltage readout. I had my DVM in parallel with the tester for this exercise; all voltages are as reported by the DVM. Under tester load, the battery terminal voltages dropped to 0.45, 0.49 and 0.65v. A "fresh" CR2032 measured 3.28v with the DVM alone and 3.19v under tester load.

So with the DVM test alone, which of the four would you have declared "good"?
 
Last edited:
signal-2022-10-17-144949.gif


I'm learning lots about battery testing. I feel like I've had plenty of new I the package button batteries that were no good for sure!
 
There are 2 types of engineers. The ones that use their education and experience and put it to use in a practical manner. And the ones that go to extremes and can't think outside of the box and say there's only one way to troubleshoot an issue. While it's not incorrect that load testing one of these 3V coin batteries can determine if it's god/bad, it's just not required for 99% of failures. When they die, they usually don't hold their voltage with any load.

Sooooo, which type are you?
 
Sooooo, which type are you?
Trick question?

The whole point of my comments, have been to let others know that using just a volt meter will work for a large majority of questionable 3V coin batteries. It should not be required to load it down. Some internet "experts" disagree. :D
... The batteries MUST be tested under load...
That's fine, if you have the required tools. I'm guessing most don't. I wonder what the "expert" thinks about those of us who have changed the battery from a 2025 to a 2032. o_O That's not what the engineers called for, but it works fine, or actually longer than the original.

I'm done with this topic, as we're closing in on site rule violations regarding open discussion.
 
Back