The E.421 was a battery operated shunter built in 1921 and used at Milan Central Station. The locomotive was built by Carminati & Toselli with electrical equipment by Tecnomasio Italiano Brown Boveri. It stood on two bogies, each with two traction motors, and had a cab in the middle. The batteries came from the Società Generale Italiana Accumulatori, were housed in two long hoods and weighed a total of 30 tonnes. They supplied the traction motors with a voltage of 450 volts.

With this equipment, the E.421 reached a top speed of 25 km/h, which made it virtually impossible to use it outside the station. Despite a continuous output of just 140 kW, the locomotive had to be charged after about an hour of shunting, which severely restricted the possible uses. For these reasons and because of the relatively complex maintenance, there was only one locomotive built. This was retired after only two years and there were initially plans to convert it for the 650 volt DC network with conductor rails of the Varese railway. After these plans were not implemented, the locomotive was scrapped in 1935 and it remained the only battery locomotive of the Italian State Railways.