Wally,
When I set one engine on the track w/ 14V to charge the battery, should the engine be "shut down" or does it need to be "live"?
Either way is fine.
I don't have a charger; should I get one?
Yes, you should. It's better to not put hours on the electronics while charging the engine's battery. I reccomend MTH's batery charger so that you don't need to remove the batteries from your engines to charge them. It may be found at this link:
www.mthtrains.com/content/50-1019
I have PRR GG-1, NS SD70ACe, and CSX FP40H, all PS 2.0. Should they all have charging posts/receptacle?
The earliest PS2 engines did not have charging jacks. Thes engines should be chaged on the rails.
The next generation of PS2 engines had 5 volt boards with 8.4 volt batteries and round charging jacks.
The third and final generation of PS2 engines had 3 volt boards with 2.4 volt batteries and rectangular charging jacks.
The MTH charger will charge both types of batteries.
This and a whole lot more is all in "The DCS O Gauge Companion 2nd Edition", now available for purchase as an eBook or a printed book from MTH's web store site! Click on the link below to go to MTH's web page for the book!