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The process of recharging a battery electric bus can be completed through plug-in (conductive), wireless (inductive) or catenary (overhead power lines) charging. Plug-in charging requires a direct connection through a power cord [39] and is well-suited to overnight bus charging, but can be used in some instances for opportunity charging. This is popular due to its simplicity and high efficiency [39]. Wireless charging relies on induction between two coils, this is better suited to opportunity buses where recharging can take place along the route without the need for a physical connection [39], such as the PRIMOVE bus where charging is carried out at each end of the route and at five intermediate stops [40]. This form of charging, however, suffers from increased charging times and relatively low efficiency [39]. The trolleybus uses overhead catenary to provide power to the bus [41]. This type of charging exhibits high efficiency but requires an extensive network of overhead cables. Table 2 shows a selection of operating pure electric buses in different locations and utilise a number of battery technologies and operating approaches. In 2015, there were an estimated 150,000 battery electric buses, mostly located in China, with a sixfold increase between 2014 and 2015 [42]. The electric bus market is growing quickly where it had a 6% share of global bus purchases in 2012 but is forecasted to grow to 15% by 2020 [43]. Battery electric bus devel- opment has been carried out all over the world with the largest shares in China, Europe and North America [44]. It is clear that some of the buses listed in Table 2 utilise more than one mode of operation to provide for the operational power requirements, such as the complete coach works bus, which uses both overnight and opportunity charging. The differences in Manufacturer Length Capacity Battery type Battery capacity Type, range Deployment location ABB TOSA 18 m 135 Lithium titanate oxide 38 kWh Trolley, on-route Switzerland BYD 12 m 40 BYD Iron Phosphate 324 kWh Overnight, 250 km Worldwide Complete Coach Works 12 m 37 Lithium-iron Phosphate 213 kWh Overnight/ opportunity, 145 km US EBusco 12 m 76 Lithium-iron Phosphate 242 kWh Overnight, 250 km China, Finland Hengtong EBus 12 m 70 Lithium Titanate 60.9 kWh Opportunity, 39 km China New Flyer 12 m 40 Lithium-Ion 120 kWh Opportunity, 72 km US, Canada Primove 12 m 44 Lithium-Ion 60 kWh Wireless, on-route Germany Proterra 10 m 35 Lithium Titanate 74 kWh Opportunity, 42 km US Siemens 8 m 40 Lithium-iron Phosphate 96 kWh Trolley, on-route Austria Sinautec 12 m 41 Ultra-Cap and Battery 5.9 kWh Trolley, on-route China Table 2. Selection of operating electric bus models worldwide [40]. Hybrid Electric Vehicles42