Peter, maybe consider waiting until @gunrunnerjohn, @Vernon Barry or another more knowledgeable electronics person weighs in here, but I'm pretty sure there's a current limiter either in the locomotive or PS2 wall wart charger that safely charges the battery/BCR. Just guessing, but it may be best to use a DC power source that's limited to probably less than 1 Amp. Using a more powerful HO DC power pack may "work", but if my hunch is correct, the damage to the BCR2 may not be readily apparent and would theoretically manifest as a long term inability of the BCRs to perform optimally.
If it was me, and I wanted to do what you're doing, I'd first ask here (like you are) and wait for a more definitive answer.
