Think there's a 1:75 gradient from Uckfield up to Crowborough & a descent from there to Eridge (not sure of that gradient). Would need some decent battery power to get climb the incline (esp if 8/12 car) from a standing start.
The Oxted Lines are quite hilly (not too bad on the electric sections) but south of Hurst Green would be interesting.
Hills are largely irrelevant to battery vehicles. The traction motors can’t tell where the electrons come from.
To put it into context.:
A 4 car DC Class 377 weighs a nominal 174t tare. With all seats taken it will be 200t give or take.
This train has a maximum power of 1.2MW.
1.2MWh of battery pack weighs roughly 8 tonnes. That would be an extra 4%. Or rather less if the ‘ballast’ is removed (the deadweight added to D.C. only units to have them in the same spec as units with a transformer).
A battery of this size would enable the train to be on full power for an hour without any recharging. On a typical Uckfield cycle, the 171s are travelling off the juice for 96 minutes, of which 25 are stationary, a further 15 or so are braking and another 15-30 minutes are coasting or on less than full power. Only about 30 minutes are on full power, if that, and that includes the hills.
Of course a train that is braking will be recharging the batteries, particularly so when going downhill. All told that leaves plenty ‘in the tank’ for a full return trip. Add in a short section of third rail at Uckfield (live only when a train is on it) for a 10-12 minute top up, and it’s really rather straightforward.