Now this is what I would do
I would hook up a current meter to monitor the current at the battery(you don't hook it up in parallel to the battery, you will kill your meter). Then, see how much is being drained. If its not much, then it is your battery. If its significant (there will always be some sort of minor parasitic draw) then start disconnecting connections until you find the drain disappearing.
Again, this is assuming the battery isn't defective and just draining itself.