[AndrewDucker]

The capacity of the connection they can saturate is in GW. The capacity they can store is in GWh.

Power generation is generally in GW, and if you're trying to work out how much demand you can satisfy, then that's what you want to know. If you're trying to work out how long you can satisfy it for then you want GWh.

[bryanlarsen]

It's even more confusing when those two numbers are the same which does sometimes happen. However, for grid storage it's more common for the GWh number to be 2-4x as large as the GW number.