While this is true, these battery solutions tend to offset the much larger externalities of the fossil-fuel based technologies they help make redundant.

The li-ion externalities is mostly incurred once when mining. Although it's still in it's infancy, recycling li-ion batteries is already possible, and supposedly profitable. Especially when you can get an enormous batch of cells of exactly the same model as you would with this project.

The biggest problem in recycling li-ion batteries is that you may need different processes for different cells, so you need to sort them first.