[syhprum]

In Maidstone before the war our local 20MW coal fired power station used Lead acid batteries for storage as did many submarines.

[alancalverd]

The batteries in power stations were (probably still are, after a major grid failure in the USA) used for maintaining emergency lighting, lifts and telephones, or to shut down reactors safely (remember Chernobyl). The US theory was that there would always be enough grid power available to restart the boilers or reactors, but when parts of the eastern grid literally  collapsed in an ice storm, it took weeks to restart anything.  Power station batteries do not feed the grid - the are too small and too valuable!

Submarines used batteries for silent running at depth - attack, not cruise. Most of the time, diesel subs run just below the surface with an air snorkel, for the same old reason - the energy density of a battery is tiny compared wth a tank of diesel fuel.