a problem I see with battery is that if the train or engine derails a battery powered engine will not stop running. with track power if the train or engine derails it stops because of the short circuit that almost always results. this is like a built in E-stop. with battery powered engines it will just keep running after a derailment which could result in a disaster.
I still dont see how I can fit a sound decoder, speaker and battery in my 44 tonner.