I've been thinking about something similar but thought that I might make a generic boxcar full of batteries. It could be tethered to any loco.
Want to use 18650's but they are a PITA to charge correctly in big series/parallel groups.
My other thought was to make a battery pack boxcar with track connection rollers, like on a lighted car. Then, just let the batteries feed power to the track where the loco in front of it would pickup the power. Thinking it might be good for my outdoor setup with the power only having to go a few feet instead of cleanly around the whole loop.
