The battery “green” stuff is all the craze but those who are pushing it are doing so for instant gratification purposes and give no care in the world to environmental damage those batteries cause during their disposal.
Ideally even with the loss of some seating. An M7 remanufactured as a M7D model “DMU” would be very valuable to the short haul commuter lines and upstarts whose lines are
1) too short to justify full
Loco haul diesel.
2) whose lines ridership doesn’t justify the cost of full electrification.
Using LI for example
A dual mode M7(DMU) would be the perfect concept for oyster bay outside of the rush hour service.
As well as the Greenport Service.
Said DMU would be capable of running on 3rd rail when in electric territory.
As for a battery-diesel-electric “multi-power MU”
I think you’d need a 3rd or 4th car married set. Each car having different components to spread the weight out.
But at what point does it fail.
Personally I don’t like the self propelled married pair concept because if you loose 1 unit you’re out 2 off the bat.
That’s just a matter of opinion I guess.