I know this sounds a bit nostalgic, but over 80 years ago Prof Drumm's patent battery trains were effectively doing 50km on a full charge. So what's with all this fancy new lithium battery technology?
Also as far as I am aware the Drumm trains used to recharge from a fixed point at Amiens Street, using a pantograph..
The more I think about it the more I fear that bi-modal battery trains will be an excuse for not providing a more comprehensive proper electrification.
Also we should not get advice from the UK on electrification projects. They have a cost over-run history worth of the HSE. So for advice go the Spaniards, the Portuguese, the French, or others who have done electrification on fairly lightly trafficked lines which does not appear to cost the earth.