Some 3rd electric rail based transit systems have regenerative braking that feeds power back into the electric rail [1], which is used by other trains that are

Some 3rd electric rail based transit systems have regenerative braking that feeds power back into the electric rail [1], which is used by other trains that are drawing power at that moment. I don't know if they use batteries to store excess, however. 1. https://www.bart.gov/news/articles/2016/news20160826 https://www.bart.gov/news/articles/2016/news20160826