Another battery-drain culprit, especially at this time of the year, is a heater fan left on low so you can't hear it. The heater fan should have been relayed through the ignition so it won't drain the battery.
The only other car I have had where the heater fan wasn't switched to the ignition was my 1934 Auburn (in the avatar). Of course most cars didn't even have heaters back then. To use the one in the Auburn, I had to open the hood and turn a valve on the head to get hot water to run through the heater core inside the cabin, which would then cook a passenger's feet most of the time. You would never forget to turn off the heater in that car.
Sorry for the digression. One of the things that fascinates me is the evolution of automotive technology and how driving experience used to be varied among cars and involve the driver much more intimately. There is such a dumbed-down sameness in all cars today. Maybe that's why I like my Alfa, which is mostly older technology that gives traditional road feel (rwd, worm and sector steering, solid axle, rod linkages, simple, clean styling) but has a little advanced, go-fast engineering (twin OH cam, VVT) thrown in to make it fun.