Car key fob lithium coin battery check voltage before replacing it

[zillah]

Dear Experts

Sometime I worked with my friend in his car wrecking yard , and sometime we need to check car key fobs that are not working if thier batteries are dead or not ,,,using Fluke 117 multi-meter and KYORITSU

Most batteries are Lithium Coin Battery size 2023, 2016,2025 (3V)

Some remotes fluke shows voltage for their batteries are very low obviously need to be replaced once we replace them they would work no drama

And other remote fluke and KYORITSU show voltage for their batteries almost 3V or 3.06V, 3.16V and those remote are not working but when I replace their batteries they would work !!!!

I want to know why new those remotes work for new batteries while with they won't work with the old batteries although voltage are still around 3v or +3V ? Isn't measuring a voltage should be a reasonable evaluation to check a battery if it good or not ? ?

Thanks

 

[SparkyChick]

It all depends on the ranges available on the meter, which one you are using and how accurate the meter is. Without regular calibration (bear in mind we generally have our test equipment calibrated every year), it's possible the meter's accuracy is compromised due to age, misuse, condition of the batteries in the meter.... there's a whole host of factors that could come into play.

 

[telectrix]

also, a battery can, if unused for a while, show a decent voltage unloaded, but as soon as a load is applied. it drops.

 

[snowhead]

Try measuring the voltage on a new battery.

A 3v will be well over 3.16v and as TLX a new one will hold the voltage whereas a used one will drop voltage under load.

 

[suffolkspark]

these batteries are like 90pence .... why bother?

 

[zillah]

also, a battery can, if unused for a while, show a decent voltage unloaded, but as soon as a load is applied. it drops.

A 3v will be well over 3.16v and as TLX a new one will hold the voltage whereas a used one will drop voltage under load.

Thanks this is what I wanted to know

 

[static zap]

A bit like reving an engine , 3.18 3.22 Unloaded Brand new
.... 3v LED torch .. Catch 22
each time you load a battery to test it ,you have drained it a little .
(Much like those duracels with test stripe !)

 

[ruston]

You can buy a simple tester that tells you the signal strength left in the batteries. The type that most decent garages have that replace the batteries as part of their service.

 

[DPG]

Testing the openb-circuit voltage across a battery (or 'cell' in this case if being pedantic - which I am) never gives a definite idea of actual power available within it. As mentioned above, the voltage can creep up over time if it is left out of circuit, but it still won't have the capability to provide enough current to operate the radio transmitter in the fob.

Testing with a load resistor is possible, but you have to be careful in choosing the value, as you don't want to exceed the power delivery capability of the battery. I wouldn't recommend load-testing small capacity batteries unless you are certain what you are doing.

Also, never ever use cheap batteries. For 2 reasons - one is general lifespan, and the other is that cheaper ones are more likely to leak and this will lead to reliability problems with the fob.

 

[grantr37]

Coin cell batteries are designed to give low current power over long durations to clocks, watches and some remote control and key fobs the internal resistance and chemicals inside can change and deteriorate with age, for cheap 10 for £1 coin cells this can happen in 2 years without any use and less with use, good quality coin cells (£3 to £6 each) have different chemicals inside and will contain silver and coltan, antimony and the likes which increase the stored energy and decrease internal resistance in alkaline coin cells. The coin cell/button battery type batteries will sometimes show 3 volts without any load on a meter or battery tester but drop off as soon as the load is connected.
Typically coin cells will operate a car locking key fob with a pushbutton for 2 years assuming use 10 times daily as pressing the button powers the small low power transmitter that pulses the code to the car, newer key cards supplied with keyless entry and push to start buttons in cars sold since 2005 will have 2 or 3 nickel metal hydride rechargeable coin cells and charge when in the card slot in the dashboard however these batteries will need replacing after about 4 years when they stop taking a charge, the keyless entry cards can also be non rechargeable in which case the duration is about 2 years as the keyfob has a higher quiescent current use and polls for a connection to the car, these low power transceiver cards (key fobs) operate at a couple of milliwatts transmitting power and a range of 20 meters or less and are the ones that criminals try to clone and make off with your car from the driveway...

 

[grantr37]

Garages and some shops will put the cheapest batteries in and charge you £20, if you can you should get a watch shop to do it or timpsons as they use good batteries or go online and buy energizer, duracell or varta ones and do it yourself.
Decent batteries will be about £5 in chemist's shops or about £1.50-£2.00 on the internet.

 

[suffolkspark]

Never had a problem with GP batteries in various sizes, their coin cells are literally 85p

 

[elsparko]

just pop the batteries on the radiator and save yourself some pennies, whenever my t.v remote is not working, instead of getting new batteries, i just pop them out and rub them on my trousers, and they work