A problem with the single battery is that it needs to be recharged at short intervals, but in city buses, that can be addressed by changing the battery at the layover time. Since the battery pack accounts for 50-60% of the cost of electric vehicles, swapping helps reduce the bus price, said the company.

The idea of running large vehicles using battery swapping was initially proposed by Ashok Jhunjhunwala, a professor at IIT-Chennai and adviser to the union government on electric mobility. But many had scoffed at the idea due to unavailability of associated infrastructure.

Ashok Leyland, India's largest bus maker, took up the challenge to prove the critics wrong by making a commercially viable bus based on battery swapping. It developed the Circuit S in partnership with Sun Mobility, a company cofounded by Chetan Maini — the man behind India's first electric car, Reva.

The bus is targeted at operators plying on city routes. City buses have fixed route kilometres, so the battery can be changed between trips.

According to Ashok Leyland, as much as 85% of the city routes in India are shorter than 35 kms. In 60% of cases, it is less 20 km. The city bus requirement in India is est imated at 7,500-10,000 a year. The company estimates that buses based on battery swapping have the potential to corner 6,000-8,000 of that market.