This particular route wasn't electrified, they mention at the end that it's electrification was cancelled after cost overruns.

Reading between the lines, this is quite a short route, and the batteries are really not particularly impressive (more than a typical car battery, but not much more), though the recharge rate is (2000kw is impressive). Batteries are very expensive (maybe less than electrifying a line, but still very expensive), but trains are very good at lugging massive weight, so if you could afford the batteries you could probably make a battery train that went genuinely long distances (more than battery cars would ever be practical for).

Though a battery fire in such a train would be an impressive and expensive lightshow.

Third and fourth rail systems are largely deprecated due to the dangers to workers.

Overhead lines are safer, but require adaptation of the formation at stations, bridges and tunnels. This is the sticking point on the Great Western main line, as the clearances were already lower before the trackbed had been raised in the 80s to give the HSTs a smoother ride, leaving no room for OHLE without expensive works.

Batteries are a compromise, and could be the permanent solution for shorter routes.