If my alternator is good, what else could cause a charged battery to drain?

What is your question?

A fully charged battery only last 2 days at most. Once the car is started it runs fine. But when it sits overnite the battery depletes. The diagnostic code reads "low voltage", but does not tell me WHERE or WHAT has low voltage. The charging system test reads "pass" on the battery and alternator with & without a load placed on the system.