2001 c240 won't start, electrical issues
 

2001 c240 ignition issue. Started after charging battery while battery cables still connected to vehicle. Vehicle will start and run fine until I turn off the vehicle and remove the key. When I re-insert key, car doesn't recognize key and won't allow me to unlock ignition until I disconnect and reconnect battery. If left over night, battery is completely drained. when battery disconnected and recharged the car starts ok. If I disconnect and reconnect battery car starts fine. Also, if I remove and reinsert ignition fuse the car will start. I hear a relay click when removing and re-installing ignition fuse, which makes me think a relay contact might be sticking and seizing until the battery is drained. I don't see any electrical items being powered when the key is removed, so I'm not certain of what is draining the battery. Any idea what is causing this?