That is why Transport Scotland are being fairly cautious on what self-powered means in the very long term.

Of the Long term self powered routes:

Stranrear - Girvan (limit of electrification) is 54 single/108 return miles - not far off battery for return trip.

Tain (limit of proposed electrification) - Wick is 116 single miles

Tain (limit of proposed electrification) - Thruso is 109 single miles

Dingwall - Kyle of Lochalsh is 64 single / 128 return miles

WHL: Craigendoran Jn (limit of current electrification) - Cairnlarich is 36 single / 72 return miles

WHL: Craigendoran Jn (limit of current electrification) - Oban is 71 single / 142 return miles

WHL: Craigendoran Jn (limit of current electrification) - Fort William is 100 miles

WHL: Fort William - Mallaig is 41 single miles / 82 return miles

WHL: Craigendoran Jn (limit of current electrification) - Mallaig is 141 single miles *significantly outside current battery envelope*

With some judicious charging points at the far end (and Fort Bill) and some long layover times then an awful lot of that could be battery with just few battery performance improvements.

(Or just rebuild a 153 and part fill with batteries and a bit of luggage space for bit of extra battery range and hook it up a one end

. The batteries will take up a lot less space than Hydrogen!)