Conversion of ten maintenance Diesel locomotives to zero emission battery locomotives, complete with on-board charging for London Underground. Operating from both the on-board traction battery and the 3rd/4th rail supply retaining the existing chassis, cab, brakes and axles to reduce compliance issues. Retaining the existing driver controls to keep driver familiarity and reduce training demands with sufficient battery power to undertake 1 day's full duty cycle. Hauling up to 240 tonnes up and down a 1:30 gradient, and travel up to 49 km/h, increasing the mass from 34 to 40 tonnes.