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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 03-08-2007, 05:48 PM   #1
jason 77
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replacing battery in key fob....

Ok so here is my first attempt at a detailed "DIY" thread, also if you mess up your own key trying to do this don't yell at me!

So I have the 2 key fobs that came with my car when I bought it used. One I use everyday and the second one has had a dead battery since I got the car. When I called the dealership they wanted like $260.00 for a new one. I did a search around here and found you could get deals and what not and possibly get it down to around $90-120 bucks.. still way too much in my book since I already had a working key.

After seeing a thread on here where another member had taken apart a key fob from a car he had already sold I decided what the hell the key was already dead anyways...

Here is the key before I tried anything..



I then proceeded to take a matt knife and xacto knife and basically carefully cut the key open along the seam where the top and bottom joined up.



Next I took a small chisel and broke the spot welds on the battery that connected it to the rest of the circuit board.



Once I had the battery out I looked at it and took the model number "a panasonic VL2020 3v" I found the exact same battery on mouser.com for $4.73. Once I got the battery is was a simple matter of soldering the new one in and making sure everything fit back together.




Before I glued it up I rubber banded the thing together and went out to my car to see if I could program it.

Put the working key in the ignition. Turn to position 2 for like 1 second then back and remove the key.

Press and hold the "unlock" button then press the "lock" button 3 times, you should hear all the locks cycle through.

Now take the non working key and press and hold the "unlock" button then press the "lock" button 3 times.

Then turn the ignition on and off again to end the programming....

I took the car for a drive to charge up the battery. Once I was certain it was all working I glued up the key again with some super glue....

Here is a pic of the key being glued...



While definitely not a hard or complicated "DIY" project I did save myself about $200 and had fun while doing it...
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Old 03-08-2007, 06:07 PM   #2
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Great job!
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Old 03-09-2007, 03:13 PM   #3
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Great job!

Thanks
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Old 05-19-2007, 08:11 AM   #4
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dude, that's fresh, you're the freakin man and will probably save more than a few people hundreds of dollars!
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Old 05-19-2007, 08:37 AM   #5
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Old 06-27-2007, 09:05 AM   #6
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Nice!

On that site I found same size batt, same voltage but a little more mAH....

http://www.mouser.com/search/Refine....RefType=Header

Hum...... Maybe a little more performance???

I think it would need more voltage rather then mAH... I am going to see if I can find the same size in 3.5 volts or 4.0.....
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Old 06-27-2007, 09:18 AM   #7
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More mAH means the battery has more capacity and will last longer (esp between charges).

As for voltage, in this case, it's possible that increased voltage will provide extended range but it's also possible that you'll damage the electronics of the key, depending on how sensitive they are. There's usually some protection for things like this but the key is made from a closed-case and not meant to be servicable so who knows. 3V ain't much and it *most likely* wouldn't hurt to increase it a bit but I would stick to the stock battery to avoid killing your key....

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Originally Posted by 04e46conv View Post
Nice!

On that site I found same size batt, same voltage but a little more mAH....

http://www.mouser.com/search/Refine....RefType=Header

Hum...... Maybe a little more performance???

I think it would need more voltage rather then mAH... I am going to see if I can find the same size in 3.5 volts or 4.0.....
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Old 06-27-2007, 09:26 AM   #8
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Yeah I am thinking the poor range might be from the battery charge drooping quickly (due to low mAH) so a little higher on that would help fix that.....

Then a little more voltage would help with range...

I would assume there is some safety factor engineered into the design so .5 volts more should hurt it too much,

and when you unlock the door your taping the button its not like your holing it with another 3 volts going through the circuit for 5 min...

The key I use the most is getting work out and crappy looking so I might give it a shot on that one...
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Old 06-27-2007, 09:41 AM   #9
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Let us know how it goes!
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Old 06-27-2007, 09:43 AM   #10
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Yeah no prob I will start a new thread with a DIY if it works and doesn't blow up....HeHe
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Old 06-27-2007, 11:43 AM   #11
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This is GREAT!!! I am SO GLAD I told the dealer no way on $200+ for a new key!!

About to order the battery, but there's 2.... which one do I need?

http://www.mouser.com/search/refine....onic+VL2020+3v


(The difference is 2 Pin Vert or 2 Pin Horiz)

Thanks!
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Last edited by TKC; 06-27-2007 at 11:45 AM.
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Old 07-06-2007, 11:45 AM   #12
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Ok, I tried this last night, but it still doesn't work. Question:

How are those metal prongs attached to the battery and what did you use to re-attach the ones from the old battery to the new battery?

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Old 07-06-2007, 12:17 PM   #13
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Ok, I tried this last night, but it still doesn't work. Question:

How are those metal prongs attached to the battery and what did you use to re-attach the ones from the old battery to the new battery?

The metal tabs are spot welded on, and I just soldered the new tabs to the old ones. I did have to putz with bending the tabs to get them to line up with the ones on the battery.... Make sure you get the positive + on the battery going to the positive + on the circuit board!!!
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Old 07-06-2007, 12:25 PM   #14
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Great! Thanks for the info! I'll try again.

The other problem I see is that I only have the one key (used car) so I don't have a spare to use in the re-programming you mentioned above. I guess I'll figure that part out when I get there.
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Old 08-14-2007, 01:07 PM   #15
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Already opened the key (made a little mess but i'll solve it later)..

anyway..

for pure personal sake i've tried with a tester to check if the battery is really drained

..full charge..

in fact the remote works 1 time on 100 try..

anyone knows if it might be related to the reciever into the mirror?
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Old 08-14-2007, 01:53 PM   #16
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my battery is dead also.. but I only have one key, I don't think I would be able to reprogram it with one key..
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Old 08-14-2007, 10:25 PM   #17
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i thought the key recharged the battery every time you turned the key? I think i read that in the manual
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Old 08-15-2007, 11:47 AM   #18
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i thought the key recharged the battery every time you turned the key? I think i read that in the manual
It does, but even rechargable batteries die eventually.
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Old 08-15-2007, 06:52 PM   #19
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does anyone know of a way to change the battery and reset the key without having to use another key?
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Old 08-15-2007, 07:13 PM   #20
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does anyone know of a way to change the battery and reset the key without having to use another key?
If so, let me know cause I changed my battery and it still doesn't work cause I don't have a second key either.

I was wondering if the dealer could do it.

Otherwise, I guess I'm just takin it and paying $250 for the new key.
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