I'm brand new to the forum, but not to cars.
Figure this. The following will draw power from the battery on an almost constant basis:
Remote Keyless Entry sensor
Any user settings, such as memory seats.
Anything else that needs to retain power to function right the next time.
So, basically, unless you have a car that is carbureted, has no radio memory, no running clock, and no keyless entry or alarm system, you're going to get a spark, even if its not visible.
My 2 cents.