Since the 1880s, battery power has been proposed for electric vehicles(Ref? ). The problem has always been that the weight of the batteries is so great that the vehicle has to be designed around carrying batteries, not its payload.
The modern milk float is representative of the most cost-effective battery vehicle available at present and the extension of this technology to trams is unlikely to attract much support.
The technology available at present would give a tram a range of 30 miles on one set of batteries. In 1904, trams were covering about 100 miles per day. Three sets of batteries would be needed to keep a battery-powered tram running even if the service were curtailed to the basic minimum.
The life of modern traction batteries is not likely to be more than 5 years and considerable quantities of waste material would be generated from battery re-manufacture. A currently available (2002) two-seater electric car has a range of typically 50Km and a battery life of 3 years. The cost of battery replacement is three thousand pounds (sterling).
The efficiency of modern batteries is between 50% and 75%; this means a tramway which served a city the size of Bath would be wasting at least 400,000 units of electricity per year. Improvements in battery technology, amounting to a factor of about two, have been achieved since the year 1900, a further improvement of about 30 would allow battery vehicles to compete with existing other power sources. Should this happen during the 50 year lifespan of the trams, it would be a simple matter to install batteries in the tram and remove the overhead wires.