How does the internal battery of a BMW key get charged?

I know the key has to be in the ignition thats how the battery gets charged. I want to know how.How does the internal battery of a BMW key get charged?My guess is some kind of electro magnetic induction.



I have a Braun toothbrush where there are no metal contacts, just plastic against plastic. And it charges somehow. So my guess is that some kind of fluctuating magnet causes some kind of energy transfer to a battery in the key/toothbrush.



I certainly don't think it is a physical contact such as with the metal buttons on the key, because this would scratch the metal after a while. So I think it is a non-physical method.How does the internal battery of a BMW key get charged?With the key inserted and the ignition turned on, whether the motor is running or not, the key's capacitor type battery is being recharged.How does the internal battery of a BMW key get charged?When its in the ignition its charging

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