whip light with onboard battery?

[Gradius]

Hi all,

I've been searching for an appropriate whip light for a rad expand.  I was wondering if anyone had any luck or has tried to use the onboard battery through a 48v -> 12v adapter to power the whip, if that was even possible, and if anyone had some helpful instructions on how to do it.

I've found a variety of good whips, but I don't want to have to mount an additional 12v battery somewhere on the bike to power the lights.

Honestly, it would be really cool if they just came up with a light adaptor with USB connections to plug lights into, but I digress.

Any help or suggestions would be greatly appreciated.

Thanks!