Hello! First post. I've searched, not found my answer (similar, but not same), then registered to get help on a simple question.
If I were to hardwire my OEM lock/unlock keyfob to be powered off 12v instead of the 3v CR2032, can I get away with a 5v "cell phone" charger, possibly with a resistor wired in series to get even closer to the 3v?

I will probably just end up using the battery and leave the buried keyfob somewhat accessible to change when needed, but that's no fun!
Thanks for entertaining this.

 

You can use a standard USB charger (5V) with three silicon power diodes (1N4001, etc.) in series to drop the voltage down to 3V. Be sure to put the diodes in the correct polarity direction (cathodes towards negative).

 

Perfect. Thanks much!

 

Thanks KJ6EAD. Helpful to know as I will be doing something very similar.