A small scale power or energy storage device could be a rechargeable battery like the Li-ion battery, acid battery, or could be a fuel cell unit (or a stack of units).

"Small" and "Large" scale are relative terms that mean different things for small users like typical consumers, large scale industrial consumers and utility companies.

For a consumer small scale would be a few hours worth of storage large scale might be a few days or weeks of typical power usage.

Commercial users that must continue to operate like oil refineries will have a plan to either replace lost power by using steam turbine drivers instead of electric motors, shutting down less important and possibly using stored power (usually battery) .