here's what happened yesterday to me:
I charged my H320 all day thru USB in the iRiver firmware.
when it said "completed" I started rockbox, and applied kosh's newest experimental build.
when I rebooted, rockbox reported the battery to be empty, and thus refused to boot. (screen went blank, device turned off right after ROLO)
the iRiver firmware reported the battery as full though.
I then listened to a few songs in the org firmware, then tried to boot rockbox, and it showed the batt as full.
Seems usb charging and battery statutes somehow dont go together very well....?