/ car key fob battery

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CPH 08 Jan 2020

Hardly ever used the spare car (remote opening) key over 4 years but it didn't work today to open the car doors. Got a new battery and it was fine. The other key used every day works fine and has never needed a new battery. Did the battery in the spare just discharge itself somehow? Someone said today at the wall that the key fob battery gets charged when in the ignition and the engine is running. Did a bit of googling to no avail. Any thoughts anyone? I'm wondering about alternating use of the keys, say a month at a time. Is all this charging stuff car specific?

Ridge 08 Jan 2020
In reply to CPH:

Seems unlikely that most keys charge from the ignition. Mrs' car is push button start and just needs to be in proximity to start the engine. If the battery goes in that it has a 'dumb' key that slides out of the fob to open the drivers door and a plug in port in the glove comparment to power up the fob so it can be started. None of my cars has ever charged up key fobs when inserted in the ignition.

IRRC Fords used to have a separate key that went in to the ignition first to allow new keys to be recoded to the immobiliser, (people kept using this as a spare and after a set number of uses it immobilised the car..).

Dax H 08 Jan 2020
In reply to CPH:

I had a van (ford I think but I have owned a lot of vans over the years) that charged the key from the ignition. Like you I swapped keys every couple of months and never had a problem. 

CPH 08 Jan 2020
In reply to Dax H:

that's interesting; thanks for that.

Rick Graham 08 Jan 2020
In reply to CPH:

On some vauxhalls, there was a procedure  for recoding the key.

Not in the handbook , a mechanic told me the trick.

From memory. Sit in the car with the door shut. Turn on the ignition  and lock the drivers door with the door button.

Worth a try.

wercat 08 Jan 2020
In reply to CPH:

look up the shelf life of the battery since manufacture and deduct some time for using it.

tlouth7 09 Jan 2020
In reply to CPH:

Mini keys circa 2008 charge from the car, but you can tell the difference because the battery is soldered in place (and they will charge you several hundred quid to replace it). The standard watch battery in car keys is not rechargeable.

deepsoup 09 Jan 2020
In reply to tlouth7:

My mind is slightly blown by the concept of a rechargeable car key.  Do these keys have some sort of electrical contact with the car, or is it a sort of wireless induction doohickey?

nikoid 09 Jan 2020
In reply to CPH:

Maybe the battery was not the problem -I remember a key fob not working, so I took it apart, rotated the battery and it worked again, ie somehow a poor contact had developed. Did you actually test the suspect battery?

CPH 09 Jan 2020
In reply to nikoid:

No I didn't test the battery. The parts dept. at the main dealer just put a new one in.

I have now looked at the car handbook...it talks about changing the battery when the remote distance starts to reduce (from 100m). There's no description of charging from the car (Vauxhall Astra).

You may well be right about a poor connection having developed.

Ridge 09 Jan 2020
In reply to CPH:

Tlough up the thread made a good point. If it's a CR2032 or similar battery it's very unlikely to be rechargeable.

stevevans5 09 Jan 2020
In reply to deepsoup:

I believe it is induction coils

deepsoup 09 Jan 2020
In reply to stevevans5:

Well I never.

CPH 10 Jan 2020
In reply to deepsoup:

I now see that Ford Transit vans have a rechargeable (in the ignition) key but they can fail so you can't get into the van. It looks like the key fob unit is sealed so you can't just replace the battery. Not good for the van owner. 

DancingOnRock 10 Jan 2020
In reply to CPH:

8-10 year shelf life. 

deepsoup 10 Jan 2020
In reply to CPH:

It does seem extraordinarily complicated, compared to changing a small button battery every couple of years.  "Ker-ching!" for the main dealers though I suppose. I guess if I were to look for a less cynical explanation, making the key a sealed unit does mean it can be properly waterproof at least.

This reminds me - I noticed the other day that the 'plip' on my van key doesn't seem to have quite the range it should, probably time to change the battery in that.

Edit to add:
Bah.  Later.  It wants a CR1220.  I have half a dozen 2032's kicking about and a blister-pack of LR44's with one missing but none of them.  I think this must be the first time it's needed a new battery since I bought the van 4 years ago

Post edited at 10:14
kathrync 10 Jan 2020
In reply to CPH:

My 2011 Mercedes Vito charges the key from the ignition.  Most newer cars seem to have keyless ignitions though, so I am assuming these don't charge.


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