Key fob dead after battery replacement

[gtsdrs]

Key fob issue. I have a '25 Air that I purchased month ago, and have driven 4k miles since (!!). Mostly good. Decided to use just the fobs for keys due to all the issues with using mobile key (phone). They've worked mostly well, or at least as designed. 2 nights ago car said "fob battery low". Having batteries drain quickly is a known issue - I decided to just go ahead and replace both fob batteries. Easy.

Next morning I went to drive car (first time since replacing). fob does nothing. I bring inside, test battery - 2.6volts. I think, hm, maybe put in an old or bad battery. Put in fresh, still doesn't work. This is both fobs BTW - each has low voltage. Car is fine and will open with phone, fob against b pillar, etc. I do more investigating to find out fob is consuming 1-1.5ma when battery is inserted (this is crazy high for tiny battery). Both fobs doing this, also. So...apparently I'd put in good batteries and they'd drained overnight. It's like the fobs are trying to (unsuccessfully) initialize or something.

Anyone else having this? I've tried all the things, checking to make sure battery is placed correctly, making sure contact, and of course, testing inside I'm making sure the contact is correct polarity.

I don't understand how both fobs could go from working to not with a simple battery replacement?

I've talked to national roadside - polite, but no solutions I hadn't tried. Gonna have service look at it in a few days, but this is seriously frustrating as using phone is terrible (as far as I can tell the phone app runs constantly when used as key?) and other solutions are clunky - using app/fob to unlock manually and enter PIN.

Thanks!

 

[socktucker]

I don't understand how both fobs could go from working to not with a simple battery replacement?

@borski has an interesting theory that the batteries aren’t really dying, but the act of rebooting it by battery swap is what is really fixing it. And I agree. On that line of thinking, I bet the car just forgot both fobs and it had nothing to do with the batteries. I would try rebooting the car, and deleting and re adding the keys fobs. Fob issues on the Air are pretty unusual.

 

[borski]

Key fob issue. I have a '25 Air that I purchased month ago, and have driven 4k miles since (!!). Mostly good. Decided to use just the fobs for keys due to all the issues with using mobile key (phone). They've worked mostly well, or at least as designed. 2 nights ago car said "fob battery low". Having batteries drain quickly is a known issue - I decided to just go ahead and replace both fob batteries. Easy.

Next morning I went to drive car (first time since replacing). fob does nothing. I bring inside, test battery - 2.6volts. I think, hm, maybe put in an old or bad battery. Put in fresh, still doesn't work. This is both fobs BTW - each has low voltage. Car is fine and will open with phone, fob against b pillar, etc. I do more investigating to find out fob is consuming 1-1.5ma when battery is inserted (this is crazy high for tiny battery). Both fobs doing this, also. So...apparently I'd put in good batteries and they'd drained overnight. It's like the fobs are trying to (unsuccessfully) initialize or something.

Anyone else having this? I've tried all the things, checking to make sure battery is placed correctly, making sure contact, and of course, testing inside I'm making sure the contact is correct polarity.

I don't understand how both fobs could go from working to not with a simple battery replacement?

I've talked to national roadside - polite, but no solutions I hadn't tried. Gonna have service look at it in a few days, but this is seriously frustrating as using phone is terrible (as far as I can tell the phone app runs constantly when used as key?) and other solutions are clunky - using app/fob to unlock manually and enter PIN.

Thanks!

How are you testing the voltage? Under load or no?

I’ve replaced the batteries plenty. Maybe you just got a bad batch?

 

[ME2U]

You did the 2 things I never do (but I can be wrong) first..I change fob battery one at a time and try it right away the second fob is kept as a backup and keep the syncing alive than IF ok and REQUIRED change the second fob battery and try it right away. I don't let the car go in deep sleep before changing them or trying them. That was true for BMW 2008-2016 with comfort access and the resync was different but if you do what @socktucker suggest it will all come back. Pretty sure...

 

[gtsdrs]

Have (kinda) the answers:

The short answer is yes, it was the batteries.

The long answer, for anyone interested - even though the current coming outta my first "new" batteries was way too sustainably high (1.5-2.0ma), it was not enough for the key fob to come out of initialization mode (that is my interpretation). These were new batteries, but had been sitting long enough to maybe be past shelf life. I purchased new batteries this morning, and both fobs work fine now. I needed to know what was happening, so I threw an ammeter on again. The (fresh) new batteries spiked to 3.5-4ma very briefly (like 1/4 second) then immediately dropped to .01-.03ma (expected current draw). Recap - the other batteries I tried just sat at 1.5-2.0ma. So... those batteries evidently couldn't supply enough current/voltage under load to "startup" the key fob and instead stayed at elevated load without completing the startup in the key fob. Also explains why putting in the old batteries I originally removed didn't work either. They had enough left to sustain the .01-.03ma, but certainly not enough for that initial spike to 3-4ma.

So...Bottom line - everything is good. In this case, super fresh, maybe even quality batteries required for that initial contact with key fob.

As a side note. I've played with phone settings and even though the iPhone app says constant location/gps is required to be turned on, it doesn't. Neither does background refresh for lucid app. YMMV on whether you can walk up to car and have everything work without waking iPhone, but I've had reasonable success so far and am encouraged that while it doesn't work as well as Tesla integration, it's not THAT bad. As it turns out, may be happy using the phone as key as long as I don't experience car waking up, etc and all the other posted ailments.

 

[ME2U]

Niiiice ! Happy for you. We still learn something. Thanks for the update.

 

[Saksak]

Have (kinda) the answers:

The short answer is yes, it was the batteries.

The long answer, for anyone interested - even though the current coming outta my first "new" batteries was way too sustainably high (1.5-2.0ma), it was not enough for the key fob to come out of initialization mode (that is my interpretation). These were new batteries, but had been sitting long enough to maybe be past shelf life. I purchased new batteries this morning, and both fobs work fine now. I needed to know what was happening, so I threw an ammeter on again. The (fresh) new batteries spiked to 3.5-4ma very briefly (like 1/4 second) then immediately dropped to .01-.03ma (expected current draw). Recap - the other batteries I tried just sat at 1.5-2.0ma. So... those batteries evidently couldn't supply enough current/voltage under load to "startup" the key fob and instead stayed at elevated load without completing the startup in the key fob. Also explains why putting in the old batteries I originally removed didn't work either. They had enough left to sustain the .01-.03ma, but certainly not enough for that initial spike to 3-4ma.

So...Bottom line - everything is good. In this case, super fresh, maybe even quality batteries required for that initial contact with key fob.

As a side note. I've played with phone settings and even though the iPhone app says constant location/gps is required to be turned on, it doesn't. Neither does background refresh for lucid app. YMMV on whether you can walk up to car and have everything work without waking iPhone, but I've had reasonable success so far and am encouraged that while it doesn't work as well as Tesla integration, it's not THAT bad. As it turns out, may be happy using the phone as key as long as I don't experience car waking up, etc and all the other posted ailments.

Fantastic root cause analysis! I wonder if others experiencing intermittent fob problems are on the cusp of peak current demand failure.

New batteries may not be good. Who knows how long they have been sitting on the stores’ shelves. I had a bad batch of batteries, all purchased from the same store.