This film primarily shows the Volvo 7900e electric buses in Harrogate, Yorkshire, UK which have their batteries top-up charged during the day at the town's bus station.
Top-up charging bus batteries at a route terminus and / or other convenient locations is known as 'Opportunity Charging' (and sometimes OppCharge). The reason for doing this is that it extends the range of the working day (ie: distance that can be travelled) without needing to carry sufficient stored energy (ie: batteries) when the bus enters service.
Batteries are very heavy and buses have a legally mandated axle weight limit ... carrying more batteries (to extend the range between charges) can sometimes mean that the overall number of passengers who can travel on the bus has to be reduced.
The battery charging system used in Harrogate involves a pantograph that lowers on to charge bars located on the roof of the bus. Some people refer to this as 'panto down'.
There is also a commercially rival system where a pantograph is stored on the roof of the bus, when opportunity charging it is raised to make contact with an overhead charging unit. Often called 'panto up' this is very briefly seen at the end of this film.
Also briefly seen in this film are the 1990s battery electric minibuses in Oxford, which to use present-day terminology 'opportunity charged' outside the railway station.