I know of a sizeable datacenter in east coast US serving the financial industry that went down due to the backup systems many years ago. It is always Murphy that gets you:
(1) External power failed, causing the building to switch to battery backup based on enormous banks of lead-acid batteries (a large room full) in anticipation of starting an array of big diesel generators.
(2) One of those batteries blew up under the sudden load, spraying an employee with acid. The other men ran to his rescue and got him in a shower real fast (he was OK)...
(3) ...but sadly, this cost crucial minutes... and the batteries ran out the second they tried to start the diesel generators... BLINK, the center went pitch black, with no way to start the diesels!