luckyrob8605,
If you have an alarm system on your bike, I can assure you that it will run the battery down, however, not overnight. I had a scooter that would take about three or four days of not having been run to take the charge off it. BC is correct in stating that you must make sure the key is turned off if you use the kill switch to shut the motor off. If it runs down overnight you should be seeing a significant spark when you hook up the last cable to the battery. If that's true, you will then need an amp meter, usually found on most multimeters, to establish the amount of current draw.
If you do have an alarm system, try disconnecting it. If you don't, start disconnecting things until you have no more spark when hooking up the battery.
I keep all my tractors, scooters and my motorcycle on battery tenders but only during the winter when they don't get used. They sell a real nice one at Walmart for about $18.00.
Let us know what you find.
CC