Twice in the past couple of days I found my MX-980 completely void of any power b/c I left the USB cable plugged in for a few hours. Isn't this kind of the opposite of what should happen, considering USB provides power?

I didn't not expect the USB to charge the MX-980, but I also do not think it should drain it. FYI, the battery was fully charged before plugging in the cable, and it only took a couple of hours to kill it.