The recommendation for pulling the fuses may not catch them all, but definately a good start. There are items that are connected to the battery terminal that have in-line fuses. I had a long term problem with came to a resolution when the car failed the emissons test.
There was a drain caused by a red wire that was attached directly to the battery terminal on my 850. My dealer did not now what the wire was for, and assumed it was for a unused accessory, so he cut it. The drain problem went away. But several months later, the car did not pass the emissions test due to the emission fan not running. It was not running because it was not powered. The emissions fan relay was stuck and caused the initial drain. Relay replaced, wire is reconnected, and no drain.