Keyless Fob - works with old low battery, not with new?

[xyberlink]

Hi,

I'm having problems replacing the battery in a keyless fob on a 2018 Fiesta and also on a 2017 Focus - same style 3 button keyless fob.

In both cases I've got the "low battery in fob" warning on the dash.

After changing the battery, the fob no longer works.

If I put the old battery back in, it works fine, hence I don't see this is a resync / reprogramming issue.

The new battery is good - in fact I've tried several from different brands - same result - no response - car won't unlock.

I've checked the batteries with a multimeter - new ones are ~3.32v (although I've tried part used ones at 3.2v and 3.1v also). The "low" battery (that works fine bar the dash message) measures 2.98v.

Has anyone else seen this issue? Any ideas welcome.

Thanks,

Paul.

 

[Janner7859]

I have seen this issue before, not in my key fob, but in my blood testing meter ( I'm diabetic ).

The meter would not work with several new batteries, but would work with the old one. I had to buy the same brand (Energizer I think)  as the old one to get it to work.

[StephenFord]

I'm almost embarrassed at asking this, but I'll do it anyway.

Are you 100% sure the replacements are exactly the same size as the original? Lithium batteries are numerated with 4 digits, the 1st 2 signify the diameter in mm, the last 2 signify the thickness of the battery in mm (just insert the decimal point) So a 2016 battery is 20mm in diameter, and 1.6mm thick.

If you made an error in the 1st replacement, you may have just compounded it with further purchases. Obviously if the new batteries are thinner, they won't make proper contact with the internal terminals of the fob...

[williamweb]

39 minutes ago, StephenFord said:

thickness of the batter

Has long as it’s crispy😂

[Eric Bloodaxe]

3 minutes ago, williamweb said:

Has long as it’s crispy😂

And it's made with proper dripping - not that healthy oil stuff!😀

[xyberlink]

Thanks for the replies.....

I've actually got CR2016's, CR2025's and CR2032's as I'm into electronics generally hence have (too) many batteries. It's definitely the CR2032's I've been putting in the Ford fobs though.

I have had the issue in other items as well - e.g. scales, but that's normally solved by using a slightly less new battery, which is what I've tried in the keyfobs also, but they seem extremely fussy, assuming I'm not missing a trick.

[StephenFord]

1 minute ago, xyberlink said:

I have had the issue in other items as well - e.g. scales,

You just reminded me, I too changed the kitchen scales last month and they initially didn't work. I simply used a screwdriver to bend the bottom prong up to make a tighter fit. Worked perfectly after that...

[unofix]

The correct battery is CR2032. It is normally a problem with cheap replacements from the likes of 'Pound Land' but if you have a new good battery with a voltage better than 3.3V then then the issue is often a very fine anti-oxidant coating that some new coin cell batteries on them.

Normally the springs of the device the battery is fitted in to 'scratches' through the coating and makes contact, but with something like a keyfob the pressure and type of springs is not enough. If you have some IPA, or Meths then give the new battery a clean to remove the coating and then the battery will make a good contact. 

[StephenFord]

3 minutes ago, unofix said:

The correct battery is CR2032. It is normally a problem with cheap replacements from the likes of 'Pound Land' but if you have a new good battery with a voltage better than 3.3V then then the issue is often a very fine anti-oxidant coating that some new coin cell batteries on them.

Normally the springs of the device the battery is fitted in to 'scratches' through the coating and makes contact, but with something like a keyfob the pressure and type of springs is not enough. If you have some IPA, or Meths then give the new battery a clean to remove the coating and then the battery will make a good contact. 

Have to agree with your analysis. It just doesn't make sense if the battery is shoving out in excess of 3v for the fob not to work. It must be down to the fob not getting the actual juice, hence bending the spring, or cleaning battery as you suggest. Nothing else makes sense.

[xyberlink]

I've now tried a number of batteries of varying brands and voltages - none have the coatings - it's decided to work with a Sony at 3.17v, which with luck will give me 8-12 months peace.

Would be nice to find out the actual cause.

[unofix]

2 hours ago, xyberlink said:

none have the coatings

Energizer, Duracell and Panasonic all use anti-oxidant coatings. I couldn't say about Sony. The coating is only a few microns thick and totally clear so would be extremely difficult  to see. Of course its fair to say that counterfeit versions never have coatings as that would add to the cost.