I own a 2002 BMW 525i and there seems to be something draining the battery. If the car is left for roughly twelve hours (i.e. overnight), the car won’t start and needs to be jumped. I recently replaced the alternator and installed a new battery, but nothing has changed. I check every night to make sure no lights are on inside or outside of the car, but unless it is started sometime within the 12 hours it needs to be jumped.
The best way to find the trouble is to place a ammeter in series with the negative battery lead and monitor the current flow. Then pull fuses one at time to see which path the drthain is on. Normal draw on a battery should be less than 80 milliamps. Make sure you let systems go into the sleep mode when reconnecting circuits.
Should have been some required testing before a battery and alternator replacement was performed.
What led you to skip a parasitic draw test?