Germany currently has about 26 gigawatt hours of battery storage. Most of it sits in home batteries with only 4.3 gigawatt hours actually serving the grid.
Building that storage already cost more than 10 billion euros and at national demand levels it only covers roughly 30 minutes of summer electricity usage.
The winter months bring what's known as "Dunkeflaute" - cold dark windless periods and higher energy usage.
To survive a 10-day winter lull (the minimum realistic requirement), Germany would need about 12,000 gigawatt hours of batteries, 470 times today's storage.
Such a system would weigh roughly 60 million tons and would be made from vast quantities of lithium, nickel, graphite, copper, aluminum and steel, all requiring intensive mining.
At current battery prices, the system would cost trillions of euros. And batteries last only 10 to 15 years, meaning the entire system would need constant replacement.
The conclusion is unavoidable...
Wind and solar require reliable backup power, renewables need oil, coal, gas and nuclear.