What you describe--charging a small battery from the track is exactly how Neils system was designed to work. I don't use it that way because my track is all one polarity (overhead wire being the other) and so I use a larger battery, and charge with a plug in spot on the engine. Neil has developed a new, smaller unit, which turns the single LiPo 3.7V into 12V. I am awaiting one to test. They won't be able to be hand built, but there are receivers and ESC's in the aircraft world that are the size of a postage stamp--but they are robot assembled, I'm sure, which means volume sales are needed to justify that cost. The time WILL come---
____________________ Fix it again, Mr Gates--it still works!"