Batteries and gas aren't really comparable so I'm guessing this means batteries are expanded at a rate 10x higher than natural gas is being expanded, which makes sense because natural gas is such a mature staple that it doesn't have that much opportunity growth.
Batteries are also not an energy source, but storage.
(Yeah I guess that's technically true of all energy sources, but batteries are more like a tank than a consumable...)
Of course adding batteries to store energy from off peak renewables to ready them for the peak is the point of this, but I would point out I don't think anything prevents charging batteries from fossil-fuel generated electricity. I wouldn't be surprised if an economic equilibrium dictates this to be the case, even.
I think batteries will be highly valued equipment as a smoothing function to help reduce heavy load wear on any kind of generating equipment to help with peak loads, regardless of what's charging them... possibly allowing fossil burning plants to run closer to a base load level at all times.
