Just picked up the car from MOT etc, and noticed the "Key Battery Low - replace soon" message came up. Service also mentioned this on their report. Changed the battery and message gone - and key still works - phew!😀

When I leave the car for service I always use my spare key rather than remove all the personal keys from the one I normally use. So this is only the third time I've used this one, the message has not come up yet on my "usual" key.

So just curious if key batteries go flat quicker when not used much?

Might depend on where you keep them when not in use. Cold affects batteries and you usual keys would most likely be in your pocket, where the warmth assists batteries. Just a thought. 

4 minutes ago, Edge of Reason said:

Might depend on where you keep them when not in use. Cold affects batteries and you usual keys would most likely be in your pocket, where the warmth assists batteries. Just a thought. 

Now that's a good thought. I do usually keep the spare in a metal box tucked away in a drawer. This last year the "usual" key has also spent a lot of time there, but it has had the occasional warm in my pocket!

 

1 hour ago, Eric Bloodaxe said:

Now that's a good thought. I do usually keep the spare in a metal box tucked away in a drawer. This last year the "usual" key has also spent a lot of time there, but it has had the occasional warm in my pocket!

 

I do the same keep them in a metal box. I changed the battery of my second key last week, just before the MOT. Easy to do, I didn't want to be charged £8 from the Stealer again. I am surprised how long they last. I don't think I ever changed them on previous cars. I wonder if it's to do with keyless start, not a proper key in a lock/switch.

Just out of curiosity, does a low key fob fail an MOT?

 

3 minutes ago, Jim H said:

Just out of curiosity, does a low key fob fail an MOT?

 

Only if it stops you driving to the test centre.

 

The keys give off a signal all the time so they are always working no matter where you keep them.   Even your spare will go flat even if you never use it.

Maybe it's something as simple as some batteries lasting better than others. This is the first time I've ever had an issue and I've had cars for longer, and used the fob much more, than this one.

My Mrs's car is nearly 7 years old, and key still working fine. A friend bought a new Golf about 12 months ago, and he mentioned recently he'd just got the warning on that. Yet he'd never changed the batteries in his 2 previous cars (Mk 3 and Mk 4 Mondeo) both of which he had for 6 years. 

My last car was a 17 plate and I had to change the batteries in both keys.   This one is a 17 as well and the batterie were fine but, for the sake of a few pence and a couple of minutes I changed them anyway.

got this message month ago and replaced the key battery at the dealer, almost two years of ownership, but this is the main key , not the spare one, I wonder what could be the status of the spare one now 😄 , you've just tipped me to go and check 😄 

i found this thread interesting as just got low battery warning on main key fob and car under 2 years old.  Struggled a little bit as worried in case I ended up breaking plastic case but managed ok and replaced myself.  

Same as other posts batteries used to last many many years but now understand that it gives off a signal all the time so will go flat quicker.

thanks for useful info here 

Changed both of mine recently - follow one of the guides on You Tube ( I think there is one on this forum) its easy when you know how, for the cost its not worth waiting - had to rescue one of my neighbours trapped in a car park when his key died (BMW Mini) luckily his spare worked.

As others have said, all batteries hate  cold temperatures  and key emits a signal or if is a sleepy key only emits signal when moved

7 minutes ago, Tiexen said:

Changed both of mine recently - follow one of the guides on You Tube ( I think there is one on this forum) its easy when you know how, for the cost its not worth waiting - had to rescue one of my neighbours trapped in a car park when his key died (BMW Mini) luckily his spare worked.

You can still unlock and start the car with a flat key battery, at least on Fords and most others. Would be a massive oversight on BMW not to be doing the same for the Mini.

1 hour ago, alexp999 said:

You can still unlock and start the car with a flat key battery, at least on Fords and most others. Would be a massive oversight on BMW not to be doing the same for the Mini.

You just have to hold the fob against the steering cowling on the Mini.  There's a key symbol to show exactly where.

10 minutes ago, TomsFocus said:

You just have to hold the fob against the steering cowling on the Mini.  There's a key symbol to show exactly where.

If I can remember, on the Fiesta you put keys at bottom of dash, near gear leaver to overcome the imobilaser. https://www.fordservicecontent.com/Ford_Content/vdirsnet/OwnerManual/Home/Content?variantid=4477&languageCode=en&countryCode=USA&Uid=G1867407&ProcUid=G1867411&userMarket=GBR&div=f&vFilteringEnabled=False

I think on our Fabia you hold it over the start button, which is on steering column where ignition switch is normally found.

Car key batteries used to last several years. Conventional remote keys only used battery power when you actually pressed the button to lock / unlock, otherwise they used no power other than a little drain over time and affected by cold. 
 

Modern keys, for cars that have either keyless start, or more so keyless entry are not clever enough to know if they are in a cupboard, pocket, or centre console of the car, so they emit a signal at all times, in case you want to use them. The car has a built in detector to decide if the key is in close enough proximity to do what you want the key to do. 
 

If you have keyless start, try getting in the car but leaving the key on the roof, the car should not start, even though it’s only 18” or so from the ignition, as the proximity sensor tells the ignition the key is not present. At least that’s how it should work. So if you were filling your car with fuel with the key in your pocket, some random can’t jump in and start the car. 
 

Unfortunately this extra technology uses the battery far more than a simple open/close switch in an old remote key. 
 

Batteries like CR2032 etc are only a couple of pounds. So it’s no hardship really. 

I would add to the above, as a crime prevention measure, if your passive key is in the house, put it as far away as possible from where you park your car, or better still keep it in a Faraday Pouch, that you can buy for a few pounds on Amazon etc. 
 

Car thieves are becoming increasingly resourceful because they can’t steal a modern car without the key that has a transponder in it. For passive keys that operate keyless entry and ignition just by being in close proximity, thieves can use a clever bit of electronic kit and stand outside your front door, detect the key in the front hall of the house, boost its signal and enter and even drive off with your car.   

1 hour ago, Edge of Reason said:

Batteries like CR2032 etc are only a couple of pounds. So it’s no hardship really. 

£4 for 10 on Amazon.

1 hour ago, Edge of Reason said:

Car thieves are becoming increasingly resourceful because they can’t steal a modern car without the key that has a transponder in it. For passive keys that operate keyless entry and ignition just by being in close proximity, thieves can use a clever bit of electronic kit and stand outside your front door, detect the key in the front hall of the house, boost its signal and enter and even drive off with your car.   

Exactly what they did with mine.   My key now lives in a Faraday pouch.   If you keep your key in a Faraday pouch check it occasionally,   I checked my last Faraday pouch by trying to unlock the car with the key in the pouch and, to my surprise and concern, it unlocked.   I changed the pouch and now, when I lock the car, I test the pouch.

Yes, I had a Faraday pouch that worked at first, but after a couple of years it seemed to have lost its Faraday principles. I then bought another and it seems fine. Not sure how it works exactly, but I assume it has a useful life before it no longer protects its contents. I can have my key in the pouch inside the car and it won’t start, so I know it still works. My spare key is in another pouch, stored in a metal cabinet. To be sure, to be sure !

If you’ve got a Ford built in the last 2 years it should have the new sleepy key. 

On 2/22/2021 at 10:17 PM, Bobr said:

The keys give off a signal all the time so they are always working no matter where you keep them.   Even your spare will go flat even if you never use it.

I was of the understanding that the newer keys have a sleep mode where they stop sending signals 20 seconds after the last detection of key movement

1 minute ago, gordonroy said:

I was of the understanding that the newer keys have a sleep mode where they stop sending signals 20 seconds after the last detection of key movement

That is the case.

Although the sensor and circuitry to detect movement, will also still drain the battery over time.

On 2/22/2021 at 5:06 PM, Eric Bloodaxe said:

Just picked up the car from MOT etc, and noticed the "Key Battery Low - replace soon" message came up. Service also mentioned this on their report. Changed the battery and message gone - and key still works - phew!😀

When I leave the car for service I always use my spare key rather than remove all the personal keys from the one I normally use. So this is only the third time I've used this one, the message has not come up yet on my "usual" key.

So just curious if key batteries go flat quicker when not used much?

Out in the car this morning and "Key Battery Low" came up - this was my "main key", the one I usually use. Fortunately I bought a pack when the first one went, so had a spare and changed it when I got home.

So both batteries have lasted more or less 3 years, irrespective of the amount of use.

On 4/5/2021 at 4:00 PM, Eric Bloodaxe said:

Fortunately I bought a pack when the first one went, so had a spare and changed it when I got home.

Further mystery. After changing the battery above, next time I got into and started the car "Key Battery Low" came up again, so I swapped it again, thinking it must have been a dud.

Was just testing the batteries out of curiosity though, wondering how far the voltage has to drop to trigger the warning. They're a nominal 3v battery, but the ones originally in the keys were showing 2.8v, remaining new ones still in my pack are showing 3.3v.

Funny thing is, the one I thought might be a dud is also showing 3.3v - wonder if I'd got a fingermark or something on it when changing it, rather than it being faulty?