Paywalled? Apologies. I wouldn't have posted it if it was paywalled for me. I'm not a subscriber.

Here is one (I hope) that isn't paywalled: https://reneweconomy.com.au/fortescue-starts-work-on-world-f... Failing that try googling "infinity train battery". It was a popular story at the time. As the story says, at least two companies are doing it in Australia.

The amount of destruction these things can cause when they lose control of all that energy is impressive: https://www.atsb.gov.au/publications/investigation_reports/2... and https://www.atsb.gov.au/publications/investigation_reports/2... They can not be stopped in a controlled fashion once they get going. The latter one cost BHP $800M from memory.

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