This happens to me a few times already. I checked the car battery and it's fine.
I read that V35 has a radio drain problem. Does the V36 have this problem?

 

I don't think the problem was actually the radio but rather the cd changer. Easy to diagnose with a multimeter, disconnect the battery and put the meter in series with it (battery - meter - cable terminal) and measure current draw. Then just start unplugging fuses for possible culprits until you discover which circuit is the offender. Really fancy meters with an amp clamp can do it as well without having to disconnect anything, amp clamps for ones like a Fluke T5-600/1000 aren't sensitive enough, needs to be something like a Fluke 1587 to amp clamp that low of current draw. Any multimeter would work find running in series though.