[RossM]

For context, Thameslink operates a route through central London, and transitions from overhead power in the north to third-rail in the south. This happens when stopped at stations and is fairly quick - the pantograph/shoes are raised/lowered around the same time as the doors open - the dwell times seem the same as usual.

As for charging, Jago Hazzard has a video on a fast-charge trial[1] for a battery-only route. As it's using a modified tube train, I'd assume it's lighter and thus requires smaller batteries, but recharging from third-rail takes roughly 4 minutes.

[1]: https://www.youtube.com/watch?v=dV441HnVI34