Lyman,
I don't know if this is what you saw, but there's a reference here to the 787's "cell hours".
Inside the 787
"The 787 main and APU batteries, each with eight cells, have logged more than 2.2 million cell-hours on the ground and in the air since the airplane entered revenue service, including more than 50,000 revenue service flight hours."
This inflates experience IMO.