Here is a brand new video on the Ray Noneya channel, recorded Nov. 18, which shows clearly it will be quite a significant battery plant---nearly 3 million square feet.
A fair part of the steel structures are already completed, partially roofed, and there are further foundations around so the work can continue.
The initial target is to produce 30 GWh of lithium-ion cells annually. That's a level close to the current output of the Tesla Gigafactory in Nevada.
Considering the recently announced EV offensive, GM will need a lot of batteries.