I signed up for the original powerwall and as it turns out it's not Tesla - it's solarcity (I get it, they are the same now). Oh and by the way you have to have the solarcity solar panels installed and running for the powerwall to be installed, which has a cost of it's own.

My guess is that this isn't any different given this text:

Powerwall 2 is a battery for homes and small businesses that stores the sun’s energy and delivers clean, reliable electricity when the sun isn’t shining.