I think the power requirements for the train might be the limiting factor tho. It's not quite the rocket equation but you can't just drain the whole battery pack on a 3% incline and get 15-30% back on the decline.

a 4000 HP train is ~ 2,000 kWatts. The average diesel-electric locomotive uses 3.5-4 kwh / mile of electricity (according to chatgpt). So to go 500 miles we're looking at 53,000lbs / 26.7 tons of _just_ battery (doubled up weight to account for non lithium). The locomotive itself can weigh 120-220 tons. A freight railcar can weigh about 100tons.

For a yard locomotive where they are just moving things around this could be super useful. For hauling freight around it's a potential? You're basically losing a freight car of cargo per 500 miles.

And I would really want this thing to be NOT made of lithium ion cuz if the train derailed it would be fairly destructive.[