Key Fob Battery Replacement = Dead Key

[Stanton]

Is it reasonable to assume that any fob battery with sufficient power to operate the locking system from, say, 50 feet (15 metres) is good for use to drive the car? It is true to say that the 'face' voltage at the open terminals could be 3 volts and still collapse when loaded, but surely the load imposed by operating the locking system from such a distance would test the battery's reserve?

I don't think the remote attempts to draw more/less current when pressing the lock/unlock buttons, but that doesn't mean a weak battery won't affect operation; the proximity sensors inside the car cause probably just as much drain. If you're trying to figure out when to replace the fob battery, just do it when you get the "replace fob battery" indicator in the dash.

 

[motco]

Yes I would do that Stanton, but it's sporadic. If I get in sometimes it comes up with the little symbol, other times it doesn't. The batteries in both of our keys are fairly recent 2032 replacements. Of course the unbranded Oriental rubbish syndrome might apply - it's hard to know when there's a recognisable brand name on the batteries. Even purchasing from a popular supplier with the name of a large river doesn't seem to guarantee quality. I'll give the milliamp test a try.

 

[GerryAZ]

I just replaced the battery in my daily use fob for my 2019 again. This is the second replacement after a total of 32 months of use so about 16 months per battery. I had a couple of new (sealed package) 2025 batteries that I found in a junk drawer which were purchased about 20 years ago so I tried them. The open circuit voltage was about 3.279 on each battery, but neither one would operate the door locks so I tried the current test noted above and had the following results:
1st old battery from sealed package about 10 mA.
2nd old battery from sealed package about 6 mA.
Battery removed from fob after receiving low battery warning for several days delivered about 75 mA.
1st old 2032 battery removed from garage door remote delivered about 350 mA.
2nd old 2032 battery removed from garage door remote delivered about 130 mA.
I did not want to shorten the life of the new fob battery so I did not perform the current test, but open circuit voltage was about 3.292 which is just a little higher than the old batteries that were too weak to deliver current.

 

[LeftieBiker]

Lithium cells, especially button cells, have a pretty limited lifespan, whether they are used or not.

 

[lorenfb]

I just replaced the battery in my daily use fob for my 2019 again. This is the second replacement after a total of 32 months of use so about 16 months per battery. I had a couple of new (sealed package) 2025 batteries that I found in a junk drawer which were purchased about 20 years ago so I tried them. The open circuit voltage was about 3.279 on each battery, but neither one would operate the door locks so I tried the current test noted above and had the following results:
1st old battery from sealed package about 10 mA.
2nd old battery from sealed package about 6 mA.
Battery removed from fob after receiving low battery warning for several days delivered about 75 mA.
1st old 2032 battery removed from garage door remote delivered about 350 mA.
2nd old 2032 battery removed from garage door remote delivered about 130 mA.
I did not want to shorten the life of the new fob battery so I did not perform the current test, but open circuit voltage was about 3.292 which is just a little higher than the old batteries that were too weak to deliver current.

A very short momentary current test (not a typical load test) will not shorten the battery's life.