Developments in soluble lead flow batteries and remaining challenges: An illustrated review

•A brief history of lead-based batteries with an emphasis on the development of the soluble lead flow battery (SLFB) is presented.•All SLFB publications to date are reviewed, providing a comprehensive introduction to SLFB research, the developments and remaining challenges.•Experience from the lead-acid battery and lead dioxide coatings industry is applied to better understand the observations made in SLFB research.•Scalability of the system is considered, involving a description of the 1000cm2 flow cell stack only available as a DTI technical report.