[Britwrench]

Rarely seen battery drain on 986 or 996 models. If the drain is that much, something is running.

Disconnect the ground wire from the battery and use an ammeter in the circuit, the current drain should be around 40-100 Ma.
To drain a battery in three hours, the drain is going to be in the AMPs region, not Ma, which is unsual to say the least.

There is something running or shorted, I would be inclined to suspect the alternator as have experienced failure of the alternator where the engine stops dead.

You need to check the ignition switch as JMatta said, it's a very common issue. You can remove the key with the engine running when they get really bad.