Maybe the train runs on re-chargeable Li-Po's as well? They are available in all sorts of voltages, I've seen them up to 11.1v (yes weird value I know). If he was using those in the train they would be easily hidden and could be re-charged in place.
Incidentally I had a quick look on ALIExpress and you can get those type of MP3 modules for the massive price of $1.18 each with $0.80 shipping lol! Alternatively Amazon (UK) so I presume USA as well has them for around £4-5 each, but of course probably available a lot quicker. Those little modules run on 5v, have a built in USB socket, MicroSD slot, 2w amplifier and some on-board buttons for things like next track, etc... Quite cool. There was also another I noticed which didn't have all the above, but is controllable by bluetooth as well as a further type intended for mounting in a car which seems to work from remote control - this latter one may be what the guy used on his station.
Amazing what is out there if you know to go looking for it...
Incidentally I had a quick look on ALIExpress and you can get those type of MP3 modules for the massive price of $1.18 each with $0.80 shipping lol! Alternatively Amazon (UK) so I presume USA as well has them for around £4-5 each, but of course probably available a lot quicker. Those little modules run on 5v, have a built in USB socket, MicroSD slot, 2w amplifier and some on-board buttons for things like next track, etc... Quite cool. There was also another I noticed which didn't have all the above, but is controllable by bluetooth as well as a further type intended for mounting in a car which seems to work from remote control - this latter one may be what the guy used on his station.
Amazing what is out there if you know to go looking for it...
Happily collecting things all my life... 
![[-]](https://www.blueplastictracks.org/images/collapse.png)