I'm just glad that I was prudent about keeping the batteries in my two MTH PS 1 engines consistently charged prior to switching them to BCRs a few years ago. I actually had gone to the trouble before that of installing the optional charging jack kits MTH sold in both engines (which was a unexpectedly involved process given the way the wire harness had to be connected) and religiously used the included wall wart to charge them both up before use on the annual holiday layout.
And I know I still have some of those 8.4 volt batteries sitting around somewhere.
