I’m concerned that you can currently get from Kirkby to Wigan, Ormskirk to Preston and Hunts Cross to Warrington on Diesel, but not from Southport to Ormskirk or Preston at all, so this would seem to have the most benefit.
I seem to recall there's curves of track currently missing at Burscough that would allow such direct trains...
Surely, surely the small number of people wanting to travel to Ormskirk via Burscough would manage the connection at Bridge/Junction? I'm not sure how easy it is these days, but it can't be that bad? I'd probably say it was better to do it via Sandhills, although obviously not for those near Burscough. Preston, yes from Southport there is probably more demand, but I cannot imagine it's much.
All that hassle does not feel worth it for the financial cost of installing batteries on 777s. Leave that area to Northern, and focus said technology on areas that could use it better. Such as extending Ellesmere Port trains to Helsby, and Kirkby trains to Wigan Wallgate.