Brand new battery dies if left for 24 hours. What could be draining the battery?

It turned out to be something that took a master BMW mechanic 2 days to find. After pulling the primary fuse box and the secondary fuse box and going thru all the relays there was still a big draw. It seems that even though it was still functional one of the seat motors was in the constant "on" position. We have a combined 50 years of experience working on BMWs and neither of us had ever seen that. Replace the seat motor and problem solved.

Turned out to be (after 20 hours of work) a shorted out seat motor. It worked but was alway in the "on" position. Thanks for your input.