All I know is that years ago when I was getting into O gauge and had found PS-1 locomotives cheap on eBay, I looked into them (This was after PS-1 was out.). I did some research and found out about the low battery issue. Now that I knew about it, I would just replace the batteries when I got the locomotives. But in my research, I found a web page (I believe it was on the old Protosounds site MTH had.) that quoted a MTH spokesman saying that Protosound locomotives could be run without batteries, and he ran most of his battery free. If I ever come across this web page again, I'll share it.
I have not actually run any of mine with no battery, but have run most of them with a dead battery (Before I realized how dead they were.) and as long as the voltage was about 7 volts, they would cycle to forward.
I'll admit I could be wrong, I am no expert, GGG is about the only one I would give that title too when it comes to PS-1, but I do make my statements based off of personal experience and what my brain foggily remembers.
