It's about 6000 Tesla Megapacks [1] for the entire US, roughly 20 square miles of land use.

"Using Megapack, Tesla can deploy an emissions-free 250 MW, 1 GWh power plant in less than three months on a three-acre footprint – four times faster than a traditional fossil fuel power plant of that size. Megapack can also be DC-connected directly to solar, creating seamless renewable energy plants."

We need more Gigafactories (regardless of manufacturer/owner), which needs demand to be proven (contracts with utilities), which allows for more capital to be acquired from capital markets to build more battery factories. Batteries are a known quantity though, versus nuclear where you can spend billions and a decade and still not produce a kWh of power.

Tesla built Gigafactory 3 in Shanghai in 190 days, from breaking ground to manufacturing validation of a Model 3. These are tractable problems.

[1] https://www.tesla.com/blog/introducing-megapack-utility-scal...

You don't even need that many if you shift demand via distributed dispatchable loads, like electric hot water heaters and EVs.

Also does your figure of 6000 Megapacks derive from total electricity consumption in the US, or just base load?

You need something to cover the idea that every few years we get a few weeks of minimal generation from wind and solar. Shifting load is a good idea, but it isn't enough. Eventually I have to add more heat to my house.

Natural gas can always be a generator of absolute last resort, and is likely cheaper than keeping nuclear generators running for those rare occasions.

How much does 1 megapack cost?

Somewhere between $250 and $400 million.