Power companies do this, but not with batteries. (Score 1)

It's called PSH (pumped storage hydroelectricity) and it's the only way to store large amounts of energy for later consumption at an even remotely reasonable cost. Basically it involves running a turbine hydroelectric generator in reverse to pump water uphill to a reservoir during off peak hours and then run the turbine off of that water during peak times for load balancing. Since nuclear and coal based power plants can't be ramped up or down quickly to match demand, pumped storage hydro is used to soak up a lot of the excess capacity that's unused during off peak hours. Obviously you're paying for the inefficiencies of turbine power generation, but they're pretty good (70-80%) and the differences in peak vs off peak pricing more than make up for this cost. No battery bank in existence can even come close to matching the amount of potential energy that can be stored in a reservoir dollar for dollar. That's probably why it accounts for more than 99% of global bulk storage capacity.