I don't think I buy BEV trains to be honest. I'm struggling to think of a proper reason why they might be better compared to normal electric trains.

But the linked article is pretty light on info, so I'll reserve judgement till more info comes to light.

The economics work out where they’re pretty low-frequency (I think less than two an hour per direction is the usual figure).

They’re also useful as a transition technology. The DART+ project in Ireland will use them for one line which will have the frequency for electrification (8 trains per direction per hour) and is already partially electrified, but is going to take a while to fully electrify (due to low bridges etc); once it’s electrified they’ll then likely be used in low-frequency regional routes.

(The realised project will use 750 uniform cars, about 200 of which will have batteries.)

They are good for infrequently used track and places where overhead wires would be in the way, like that very Tesla employee shuttle on it's own track and container ports.

It's not the best way to go for mainline track and not suitable for long distance high speed trains.

Ireland is going to use a particularly unusual one for the Dublin-Belfast intercity route. It will have batteries, _and_ diesel generators, _and_ will run off overhead lines, in two voltages. The context is that parts of the line will take a while to electrify; it will initially run on overhead, battery, and diesel, then just overhead and battery as the lines are built out, and then hopefully finally just overhead.

If it's infrequently used, a dual mode diesel-electric can fill that use case today.

Expense is correlative to scale, likely it's cheaper to deploy pantographs than battery factories.

Why did India build a high speed freight corridor with overhead power when they could have used batteries instead? Because the quantity of battery to power the trains doesn't exist, and overhead wires do.