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Discussion Starter · #1 ·
Key fob remote battery got weaker over a few weeks, and finally died completely this week. Searched around for a fix, most drastic was to cut it open to replace the battery.

Wanted to confirm that it was not a charging problem before replacing a perfectly good battery.

Consolidating info i found on a few other threads on this board, and others.

Step 1: Do not cut the key fob open.

Step 2: Check fuse #57 in the trunk, 7.5 amps for the fuel door. Somehow connected the charger in the steering column. Replace if blown. This should confirm that it is a charger problem, not a battery problem.

Step 3: Put your key on a sonic care charging base, it should charge it. Or just drive, and allow it to charge normally in the car. 30 hrs for a full charge, 30 mins for 15 presses. I put mine on the sonic care over night, as it was completely dead, next morning it not only worked, but had range i have not experienced in weeks.

Step 4: Post on M5 board.

Step 5: Carry on.
 

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There is something different with those sonic chargers. Not to suggest that these cars have a smart charger for charging our keys. I have a dead Xbox controller battery, so says the Xbox because it won't charge it, but if I drop the battery on my charging plate the battery charges and works as long as a new rechargeable.
The mysteries of batteries never ceases to amaze me.
Think I will have to try my key and see if it works better as it's current range is 20 feet. Thanks for the idea.
 

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Discussion Starter · #5 ·
Edit Add.

Step 2.5 After replacing blown fuse, insert key into ignition, start car, let key charge for a few mins (or drive around) to see if it took a charge to confirm that the fuse was the culprit.

Sailor and Auaq, did the sonic care charger work for you?
 

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Link to the sonicare charger you use/recommend?
But Shady, that would be useful information. What do you think this is Facebook? :laugh
 

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Sailor and Auaq, did the sonic care charger work for you?
I tried it once with just the keys on the pad and I am not sure there was much of a difference with how far I could activate the locks. I then just got in the habit of dropping the keys and phone on the pad at the end of the day. Today for the first time (mainly because I forgot and am in the habit of 20 feet) I hit the button across the street and likely 7 cars down the road and it lit up and unlocked.
Think the keys on the pad with the phone will be my new habit.
 

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Discussion Starter · #11 ·
I tried it once with just the keys on the pad and I am not sure there was much of a difference with how far I could activate the locks. I then just got in the habit of dropping the keys and phone on the pad at the end of the day. Today for the first time (mainly because I forgot and am in the habit of 20 feet) I hit the button across the street and likely 7 cars down the road and it lit up and unlocked.
Think the keys on the pad with the phone will be my new habit.
Awesome, my hypothesis is the battery never full charges, since (according to the factory) it takes 30hrs for a full charge, 30 mins for 15 fob presses. Since i typically drive 30 mins and use the fob a few times in between, it just kinda slowly fades over time.

You are talking about a wireless charging pad for your phone?
 

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Not sure what it is? A pad you plug into a wall and when you put things with batteries in them on it they are magically charged without being plugged in themselves.
 

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Not sure what it is? A pad you plug into a wall and when you put things with batteries in them on it they are magically charged without being plugged in themselves.
I believe it is called "inductive" charging.

Regards,
Jerry
 

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Do these batteries ever simply go bad? I made the mistake of opening my spare key and trying to solder in a new battery. Complete fail, you need five hands and for some reason the solder doesn't stick.
 

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Do these batteries ever simply go bad? I made the mistake of opening my spare key and trying to solder in a new battery. Complete fail, you need five hands and for some reason the solder doesn't stick.
Soldering isn't very difficult on the big stuff, when you get into the small parts it gets difficult.
 

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Link to the sonicare charger you use/recommend?
I got this one on eBay for $9. Before, I would need to get within about 3 car lengths of the Beast in a wide open parking lot. Just now, after a day on the Sonicare, I could unlock it just past 2 houses down the block with it parked in the garage. Here’s a link to one on ebay.

Holds the key nicely.
D802BE2C-DCFF-4AD8-B590-50A71D485FC1.png
 
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So this just happened with my E46 key fob, remote function gradually died. Charging on a Sonicare did not fix the issue. My fuel door locks/unlocks normally. Did some more searching and found a fantastic youtube video on battery replacement:

https://www.youtube.com/watch?v=JGeIqQ3oSFI&t=335s

Also good info on this link:

https://www.bmwgm5.com/bmwgm5/kf_battery.htm

So I decided to give it a go on my E39 spare key which I had failed on previously. Got it done and now have 2.9 V on the leads. The key will now start the car and lock/unlock manually but I can't get it to sync. My primary key is synced. Not sure what the problem is.
 

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Which car keys are rechargeable? I know on my wife's E92 that is rechargeable, but I didn't think the E39s (and I would also assume E46) were rechargeable key batteries. Also mind posting a photo of it and how you placed it on the charger? I plan on trying this tonight on my spare key as it is very weak.
 

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Charger placement see post 16 above.
Any key that is sealed and you have to cut open has a rechargeable battery. But before you get out your knife try the charger. Also check that your fuel door locks and unlocks.
Read what bmwgm5 writes in the link I attached. He says almost every key he gets has a normally charged battery in it.
 

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Is there something unique about the Sonicare charger that makes it work, or will any inductive charger work? I have a dead key that I am trying to troubleshoot.
 
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