Looking for info on the key battery charge function

[AceEngineer]

Does anybody out there have knowledge about the ring antenna in the ignition switch? I’m of a mind to build a standalone charger for the battery in my keys. My spare key goes dead and then I don’t drive enough to get it sufficiently charged and my other key barely maintains a charge because I drive my X3 so little. I plan to 3D print a holder for the standalone charger and buy another ring antenna. I know the ring antenna is dual purposed so it also reads the ignition interlock chip in the key, but I think the data signal isn’t required for the battery charge function. The charge function is probably a sine wave for efficient power transfer. I’m hoping somebody has some info about the signal so I don’t have to tear into my car to measure the signal on a scope. How about it, any experts have some useful knowledge?

AceEngineer