Currently, battery technology isn’t sufficient to power trains due to the heavy loads and long distances needed and probably won’t be possible for quite some time. Rail electrification is a proven technology available today.
The expense of electrification in the near term has to be weighed against the real total costs of delaying. That's where the Solutionary Rail argument, while still a very minority outlook, has its most important contribution. Overhead catenary is not only a proven technology, but the only foreseeable way that we can power long distance land trips of freight and passenger through non-fossil fuel based technology.
Overhead catenary is the only proven zero-emissions way to move a line haul freight train that consumes as much as several times more energy (15-25 MW) than a passenger train (1-10 MW).
That said, we support research and development efforts on all forms of zero-emissions transportation. There could be plenty of room for hybrid locomotives that could benefit from batteries- not only electric- diesel hybrids made more efficient from on-board batteries (like a Prius), but also electric locomotives that could use both batteries and overhead catenary. The battery/capacitor-catenary hybrid concept offers many opportunities: for areas with relatively short distances of incomplete catenary infrastructure (bridges/tunnels that have clearance issues perhaps), as well as backup even with 100% catenary system. The new "battery-trains" in Japan and Europe are of this type:
Ultra-capacitors are used to deliver large amounts of energy in a short time, but not able to (or intended to, even) store large enough amounts of total energy to power a vehicle over significant distance. Batteries also lack the energy storage capacity, charging time, lifespan, and cost effectiveness to power automobiles on a large scale- yet alone trains.
Non-continuous-power technology is only used on a very small number of light rail lines in the world. All are in temperate climates.
There are ups and downs in between, but in general, the average grade ascending from Minneapolis to Summit MT is 0.8%. The maximum grade is 1.2%. A 60 mph train needs about 4 horsepower per ton (3 KwPT). A bulk train needs 2 HPT (1.5 KwPT) to keep up 30 - 40 mph over most of the line.
A high speed truck shuttle train as we envision would be around 3240 Tons (assuming 20 Megaswing cars accommodating 40 trailers). A 3240 ton 60 mph train would need 9.7 MW. A 14,000 ton grain train would need 21 MW. This is just not going to happen with batteries, capacitors, flywheels, or any other kind of non-continuous power. In addition, without regenerative braking, the excess power of eastbound trains must be dissipated, not used to help westbound trains. In winter, trains would need around 15% more power yet.