Germany would require a ballpark of 100 MILLION tons of Teslas Megapack grade batteries to run on battery for 2 weeks - which is even shorter than what we had to endure due to “Dunkelflauten”.
In any case, at $100/kwh, it would cost $250bn (EDIT: $25tn sorry) in batteries and maybe the same in installation costs to power Germany for 6 months a year. At the lower $20/kwh price tag it would be more like $5tn, compared to Germany's ~$4.5tn GDP. Over 10 years it could be done.
(And 6 months' storage is maybe too much anyway)
This isn't to say they can't import it from elsewhere, they just can't make any of their own. Adding more capacity wouldn't do anything, it would take an incredible amount of batteries to handle the more extreme end of those "dark periods".