[BNaylor]

It sounds like you have parasitic drain which can be caused by any electrical problem and could be complex to troubleshoot and resolve. But you should have the retained accessory power - RAP feature as do most if not all late model Buick models.

Retained accessory power. Power windows and radio remain operational after ignition is switched off for 10 minutes or until a door is opened. Doesn't make sense for the radio to draw that much as stated or the cause if the RAP is working properly. The RAP relay is controlled by the BCM - body control module.