Really daft question, but can the central power car be engineered not with a diesel prime mover, but a very large battery pack, so it is effectively a battery loco? Surely 15-20 tons of battery or whatever delivers a lot of range....and can charge on the 25kv?
Or just not enough to get down the various off grid bits (and back!).
The very best lithium ion batteries have an energy density of approx 230Wh per kg. So 20 tonnes of battery will provide 4.6MWh of storage.
Without knowing the fuel capacity I of the diesel version, I can't work out an equivalent range, but it's unlikely to be practical. The diesel engines have a max output of just under 2MW. Let's say they average 50% output. So our battery can store around 4 hours worth of power. Maybe just about enough for a round trip Norwich Cambridge and return.
Charging would be interesting. You wouldn't be able to pull more than about 5MW off the overhead, so it's going to take an hour to charge.
And that's assuming there's space for 20te of batteries, which once packaged with control electronic and thermal management is is going to take a lot of space.
FWIW, I don't believe batteries are the future for trains or cars. For sure there will be some small number of trains run on batteries, bit for lost applications it won't make economic or operational sense.