Charging Key with Apple Watch charger

[ItsGibson]

I set my dead diamond shaped BMW key on my Apple Watch charger for an hour or so, since the Apple Watch also charges by induction, and it worked for a few minutes. Going to see if leaving it on the charger all night will charge the key good enough to last me a few days. Will update post tomorrow after work to tell you guys if it worked or not.

First post on here BTW

[TonyAngel]

I'd be careful with that. I do not know what protection circuitry there is in place for the watch charger or the charging circuit in the car, or in the key, for that matter. I also do not know at what rate the car charges the key or the watch charger charges the watch. I do know that all lithium based rechargeable batteries are limited in terms of charge rate. For many batteries, that limit is 1C, or 1X the capacity of the battery. If the key battery is something like a 70mAh battery and it's max charge rate is 1C, then the most it can handle is 70mA per hour. If the battery in the watch is, say, 300mAh (arbitrary figure but works for this example) and the charger charges at a rate of 1C or even 1/2C, that is going to overheat the battery in the key and will likely lead to a nice little fireworks show, not to mention the loss of a $200 key and what ever else gets toasted.

Of course, I could be totally wrong, but food for thought.

[ItsGibson]

It did charge the key a little bit, but not very much. Left it on the charger for about 9 hours and got a few unlocks out of it, but it seems to charge more quickly now. There was no heat at all on the key when I removed it from the Apple Watch charger. Doing it again tonight to see if it'll charge it any more.

[TonyAngel]

If leaving it on the charger for 9 hours only got you a few unlocks, it isn't working. Why don't you just drive the car with the key in the ignition.

[ItsGibson]

The reason it didn't work well is because the battery is probably 6+ years old and can't hold a charge. It's not very hard to understand that batteries don't last forever, no matter how long we sit it on the charger if it's old and worn out it won't charge much. The only reason I tried it in the first place is to see if it charges it at all. I put it on the charger when it was completely dead and when I took it off in the morning it worked for a little bit, which shows with a battery in good condition it should work, might take a little bit longer than some other methods but still.

[flyfishvt]

Replacement batteries are super cheap on eBay. I just bought 2 for $7.50. Free shipping.

its a VL2020

[ItsGibson]

I'm going to buy a new key before I attempt to do that. I don't want to be left without a key if I mess it up.

[flyfishvt]

My car came with 2 keys. One of them was taken apart in an obvious attempt to replace the battery or fix the battery. I just installed one of my new batteries and went through the program procedure. Both keys lock and unlock the doors and the trunk. As an added measure....I recently retrofitted the car with Factory Alarm system and that arms/disarms as it should when the doors lick/unlock. Now I need some superglue to glue the 2 halves together.

When you replace the battery the positive side faces up as you're staring down at the circuit board. It says +3. My batteries came with a flat post welded onto each side. I broke those off.

[ItsGibson]

Ever since I've been charging the key fob on the Apple Watch charger it works a little bit better each day. It still needs a new battery but I've definitely been getting more battery power out of the old worn out one since I started. The first day it only had the power to unlock it a few times, not even lock or even open the trunk, now on day three and I'm definitely getting more use out of it. Not getting the range I want but it's not bad for not having to buy a new key fob or battery.

[flyfishvt]

I wonder how long that old battery will hold a charge. I'm very surprised at how terrible the range is on these key fobs. My e36 alarm had much better range. I get about 20-30 feet with this e46. That's it.