What drains the battery while the e430c is turned off?

[aDavid]

My Edge 430c is maybe 8 months old and not used a whole bunch (infrequent travel, etc.). After it's been turned off for a few weeks, the battery level goes down to around half. Last time, it was 4 weeks since last Win updates (recharged to 100% then), and the machine wouldn't even turn on using battery. I make sure it is totally off with no blink, and unplug the mouse and anything else.
Is there some component or activity (other than CMOS) that continues a trickle-drain even after total "shutdown"?

[RealBlackStuff]

Maybe your USB is set to "Always ON" in the BIOS?