[a real Sheila]

(forgive my lack of knowledge of proper terminology)

according to the 60 Minutes story-

-One BOP battery was bad and had not been replaced.
-One BOP test was not conducted properly and resulted in a large rubber seal being damaged to the point that large chunks of rubber were coming up with the mud. This was brought to the attention of someone high up, but that person decided to forge ahead.

[Cold Heat]

The batteries probably were not replaced yet because they have redundancy in the requirements. One battery is not a big deal and the BOP was wired to power from the rig when they actuated it from the control room. The batteries come into play only if the rig is somehow detached from the BOP. It apparently tried to shut off the flow but jammed before it was detached when the rig sunk. At least this is how I see it from after sinking interviews..

This is where the cement job will come into the investigation, and also where the inspection of the drill pipe and casings will be important to determine the root cause of the BOP failure.