While shooting a session today, my Canon EOS 7D shut off without warning. At first, resetting the battery grip did the trick, but a few minutes later, even removing that and swapping around batteries resulted in the same ominous flashing battery icon in the top screen. Quick searches of the internet made it sound more and more like an expensive appointment with Canon repair.
After cleaning, testing batteries and resetting everything I could think, I was left looking at the same flashing icon. However, in digging depper around the web, I saw a few mentions of this issue and a failure of Canon to secure screws internally; one in particular (HERE) offered an invaluable lead to a solution and a detailed video to repair the issue: a lose screw inside the body of the camera itself shorting out the board.
Spreading the word that if you are seeing this issue, this may solve your problem. Thanks to both the site above and John Clark of Pelagic Visions Marine Imaging and Blue H2O Cozumel Watersports, who created a 15-minute repair video, embedded below. Within 20 minutes, I was back in business and saved myself $250+ in repairs!