Update: First, it is a Canon battery grip. I was able to determine it was not the cause of the problem, because the problem persisted even without the grip attached.
I e-mailed Canon tech support, who at first misunderstood my question and thought I just had a rapid battery discharge issue. They suggested rebooting to see if that solved the discharge problem. It did not. I already knew why the battery was draining so fast, because the camera wouldn't turn itself off. So they recommended I send it to Canon factory service. Which I did.
Turns out the problem was a bad main circuit board, and the solution was to replace the circuit board. That ain't cheap, but it ws necessary. I thought about not getting it replaced and just trying to learn to turn the camera off manually more often, but I figured if the circult board was bad something else would randomly go wrong eventually.
So I expect the camera back today, and I expect it to work just fine. I should know better about expectation, but there you are.
Hope this is helpful to someone else....
gc
