Disconnect the Negative battery terminal, set your DVM to its Current scale and connect the leads, one to the cable and the other to the battery post. Open all doors and the hood, WALK AWAY for 15 minutes so everything shuts off, then without changing the status of anything, closing doors, etc., then go to the meter and read the display. You want a milliamp scale. 1000 milliamps is 1 amp. You should be seeing loads when the car is sleeping of something about 100 milliamps, this is 0.1 amp, your car should be able to support this kind of load for a very long time.