At the time of the C5's launch, Sinclair described the C15 as having "a futuristic design with an elongated 'tear-drop' shape, a lightweight body made of self-coloured polypropylene and a single, possibly 'roller' type rear wheel".[1] It would have been launched at the 1988 International Motor Show in Birmingham following a development programme costed at £2 million. Unlike the relatively conventional technology used in the C5, Sinclair intended to use sodium sulphur batteries with four times the power-to-weight ratio of lead–acid batteries to give the C15 much greater speed and range – over 180 miles (290 km) on a single charge. It would have had approximately the same dimensions as a conventional small car, measuring 3.5 metres (11 ft) long, 1.35 metres (4 ft 5 in) high, and 1.35 metres (4 ft 5 in) wide.[85] However, it could only have worked if sodium sulphur batteries had realised their promise.