If you're interested, the context is that capacity was historically used in the utilities industry to refer to generation capacity, which is in MW or GW. E.g., the capacity of a power plant could be 500 MW, which for the decades of power production preceding renewables, could be sustained indefinitely as long as you're feeding it fuel.
By extension, when you talk about battery capacity in the context of the electrical grid, you're talking about the MW or GW of generation that you can replace during peak loads. The ability to distribute batteries across a grid to meet peak demand (and defer infrastructure/peaker plant construction) is the best way (today) to justify investments in batteries.
If you're interested, the context is that capacity was historically used in the utilities industry to refer to generation capacity, which is in MW or GW. E.g., the capacity of a power plant could be 500 MW, which for the decades of power production preceding renewables, could be sustained indefinitely as long as you're feeding it fuel.
By extension, when you talk about battery capacity in the context of the electrical grid, you're talking about the MW or GW of generation that you can replace during peak loads. The ability to distribute batteries across a grid to meet peak demand (and defer infrastructure/peaker plant construction) is the best way (today) to justify investments in batteries.