The sidebar on this article claims efficiency "up to 99 percent". OK, but what is typical? https://www.dailymail.co.uk/sciencetech/article-10982885/Worlds-work

The sidebar on this article claims efficiency "up to 99 percent". OK, but what is typical? https://www.dailymail.co.uk/sciencetech/article-10982885/Worlds-working-sand-battery-store-green-power-months-time-installed.html https://www.dailymail.co.uk/sciencetech/article-10982885/Wor...