We upped John's battery applications a notch to a pair of battery powered Catrike Dumonts (in my profile), exploring the old R.O.W.s of abandoned railroads at 30 mph.
Quite a variety of Battery R/C controls are available. Many folks have been choosing the non sound units due to the economy and the fact each set includes it's own remote key fob style controller. Five basic sets will provide five controllers which means five visiting folks can each run their own power unit which can also have added basic sound features. All that for under $100 each, plus a battery. Full feature units can be had for around $300 + battery and install.
Plus you will not need a $800. transformer. Also, no track wiring at all, no blocks or power zones, no insulated rails, any kind of complicated track work, turntable reversing is seamless.
I added several extensions to my RR and have no intention of running any track power to them.
