How can I determine what kept my macbook pro awake until the battery drained? I left my laptop unplugged last night and woke up to 0% battery. This is not usually what happens. Is there a way I can find out, this time or next time, what caused that? I assume something was running that prevented it from going into low power or sleep mode.
Run the following in Terminal:

pmset -g log


You'll be able to check if there was some activity during the night.