Hi...I have exactly same problem with my is220d today .
Like the original poster said all the electrical went dead despite the battery is good. Recovery engineer tested all the fuse and tried to jump start but no luck. Another similar thing is after unplugging the battery terminals it briefly give power back but when I pushed start button, everything went dead again.
Since the post was never updated I m dying to know what happend after Lexus couldn't even figure out what happened to your car.
Could u please tell me as I feel hopeless with this situation.
