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Old 05-12-2020, 09:09 PM
Join Date: Nov 2014
Location: SF Bay Area
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oldskewel is on a distinguished road
Diamond key battery repair, other options

I have a 2001 E53 with 4 keys:
- 1 regular diamond key
- 3x key fobs made from diamond keys bought off eBay, keyless entry reprogrammed by me (not EWS), with valet keys bought from online BMW dealer (with EWS chips as provided by BMW). As shown in this photo.

Name:  diamond key fob.jpg
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Things worked great for about 5.5 years like this, but now two of the 3x key fobs have been appearing to not charge / hold a charge. I understand how they are supposed to recharge, and they worked for a while, but are now failing to work. I think the rechargeable batteries are done.

I want to replace the rechargeable batteries in those fobs. With this setup, the EWS chips in those fobs are not used; the ones in the respective valet keys are the ones the car uses. I have read online here that the tough part of diamond key surgery is to avoid destroying the EWS chip, so in my case that is not a concern.

Any detailed instructions on sourcing that battery and doing the surgery?

Alternatively, maybe easier and better, maybe I could transplant the remote/fob circuit board into a new eBay housing, maybe even with a replaceable battery vs. rechargeable. Has anyone done that?

Not looking for a repair service or programming instructions.
2001 X5 3.0i, 190k miles, AT, owned since 2014

Last edited by oldskewel; 05-12-2020 at 09:17 PM.
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Old 05-12-2020, 09:27 PM
wpoll's Avatar
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My guess would be that there aren't actually charging very well, despite the 5.5 years you gotten from them.

Because the diamond section is hanging down, away from the ignition antenna ring, the charge current will be greatly reduced. The strength of the RF field around the ignition ring drops off as a square of the distance...

Might be easier to try a full (one or two day) charge on one of the units not currently working - although it may be as you suggest and the batteries are done.

You can charge the key fob battery with cheap USB smart watch charge, like this (courtesy of Crowz)


Or Andrew's trick with pins...


From these threads...



If the battery is totally flat, you may still need to re-initialize the fob after charging...

*edit* Here's another video... https://www.youtube.com/watch?v=kC68Z7CP2XM
2005 BMW X5 3.0d (b 02/05)
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Last edited by wpoll; 05-12-2020 at 09:32 PM.
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Old 05-12-2020, 09:31 PM
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so to be clear, the 2 of the 3 key fobs still start the car fine, but they no longer lock/unlock the car, right ?

They start the car because the valet key is fine
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Old 05-12-2020, 10:40 PM
Join Date: Nov 2014
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Originally Posted by Effduration View Post
so to be clear, the 2 of the 3 key fobs still start the car fine, but they no longer lock/unlock the car, right ?

They start the car because the valet key is fine
The key fobs don't start the car. But the keys do , and all 4 do so with no problems at all, as they have done for 5.5 years. The EWS chips (3 of them in the 3x valet keys, 1 in the full diamond key), etc. all work just fine.

The 3x EWS chips in the key fobs are still there but are not relied upon by the EWS, and do not confuse the EWS as long as a valid key is present. The only problem is with the rechargeable batteries in the key fobs (2 of the 3). Because those batteries are bad, the fobs will not work consistently to be programmed or work to use the remote entry functions.

And again, to maybe clarify, those key fobs all began their lives as BMW diamond keys, then found their way to eBay where I bought them, cut the keys off, thus creating fobs out of the diamond keys. Then I reprogrammed them to do the keyless entry, programming all keys consecutively using Qsilver7's often posted instructions on here.

Over the 5.5 years I've had this car and these keys, I have periodically "manually" charged them by putting them in/near the ignition key cylinder, held in place with masking tape on a key in there to the ON position, left there for a day or so, with the car on a charger to maintain the 12V battery. From paying attention to them working or not, and the behavior coming and going slightly, I'm fairly convinced the batteries themselves are due for replacement. With 4 keys/fobs, sometimes one would not work, which I'd attribute to insufficient use/charging, so I'd do this procedure. Lately, after doing this, the two failing fobs have not worked consistently.

Good point by wpoll above about the key+fob arrangement being less exposed to the induction field than with a diamond key. True, but it has worked well enough for a few years, and in my forced charging setup, it is right within the cylinder of the charging coil. So I don't think weakness of charging is the problem here.

BTW, so far, the following youtube video solution is looking like the leading candidate, and it looks easy enough to do, so I think I'll just do it. Was expecting there was a guide here on xoutpost somewhere that I was somehow unable to find.


(but I'm not sure if he uses the right battery. Panasonic VL2020 appears to be the spec as long as it has the right connection geometry - 90 degrees apart)

Also, found an interesting comment on a not-so-good youtube video:
"Hi there. I worked for BMW for many years. as an engineer. Can confirm our diamond key fob introduced in 2000 models (as used on e53, e46, e39 etc) most certainly contains a rechargeable (vanadium pentoxide) battery, charged through electromagnetic induction (via EWS ring antenna as shown in the video). Like all rechargeable (secondary) cells, capacity decreases as charge cycles occur. Most diamond fobs will last 10-15 years with normal use. Full recharge (ignition must be in position 2 or 3) from empty takes ~30 hours. 1 hour of charge typically gives 15 lock/unlock cycles (on completely flat battery) depending on age of course. Replacing with a primary cell (non-rechargeable) not recommended."

And more on the vanadium pentoxide cathode he mentions:
2001 X5 3.0i, 190k miles, AT, owned since 2014

Last edited by oldskewel; 05-12-2020 at 11:22 PM.
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Old 05-12-2020, 11:18 PM
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Ive repaired both of my e53 keys you can search xo to try to find my posts about it. Opening is the most difficult part and I had to reflow solder joints before they came to life.

I replaced the battery of one but the other the battery was fine (stunning for a 15 yr old car). You can test the voltage with a couple well placed pins poking through the rubber seal in the button. I show exactly where.

The proper battery should be easy to get on amazon pay attention to the angle of the pins I think they are 90 not 180.
E53 / M54 2001 3.0i gas LHD (pair of them: his & her)
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Old 05-13-2020, 02:47 AM
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I cut open one of the fobs. Not as bad as I thought it would be. Used a utility knife with a sharp blade.

Confirmed the battery is Panasonic VL2020 with the prongs at 90 degrees apart. Bought two of those off eBay, which surprisingly said the chemistry was lithium vanadium pentoxide.

Measured the battery voltage at about 2.6V, even after recent charge attempt. Attached a pair of AA batteries to bring the voltage up above 3V, and was able to get the (previously appearing dead) fob to program and operate as it should. So I think replacing the battery will be helpful in this fob. I'll wait to see how this one goes before cutting open the second bad one.

That youtube video I linked a few posts up seems pretty accurate other than that he uses the wrong battery as a replacement. Good enough though, I guess.
2001 X5 3.0i, 190k miles, AT, owned since 2014
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Old 05-13-2020, 03:00 AM
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Location: Saskatchewan Canada
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80stech is on a distinguished road
I agree that the original batteries are really really good and is more likely you have a solder joint problem somewhere especially on the buttons. The odd battery does need replaced though AFAIK.
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Old 05-13-2020, 07:00 AM
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Have you tried charging the fobs with for example electric tooth brush charger?
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Old 05-13-2020, 10:06 AM
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I believe he said he tried to charge in the ignition key. If they could get charged via aa (that's a very good trick) I have a bench power supply so I can limit the current but since 2 AA close to 3v just a little higher when new it prob is very close to recommend amount.

Before glueing or screwing back together I would make sure they take a charge in the car. Tape it together where you still have access to the bat (maybe solder some pigtails on the battery leads so you can plug in the ignition and observe the voltage rise.

Before I reflowed my solder joints the symptom I had was the remote function would only worth within a minute or two of being on charge. Either from on my bench supply or in the ignition.

It was so confusing. I could lock the car leaving and could immediately unlock and re-lock but if I left and came back no go.
E53 / M54 2001 3.0i gas LHD (pair of them: his & her)
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Old 05-13-2020, 10:30 AM
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I used a wireless toothbrush charger to keep my FOB battery recharge when I had the X. Maybe you should try that.
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