Rich,
Will running or idling an engine recharge these (don't think the OEMs were NiMh) sufficiently with an hour or so run time, or could this potentially take take hours to do so? The instruction booklet calls for the OEM batteries to idle for 8 hours to recharge!
As long as a PS2 engine is receiving power from the tracks, its battery will charge. MTH's battery charging instructions are based on a completely discharged battery. In that case, 8 hours for a full charge is reasonable.
For instance; if an engine has been on the shelf 6 months (or longer) would I need to remove the shell and recharge using an external battery charger?
No, you should charge it using an MTH battery charger (preferred, assuming that the engine isn't an early 5 volt board model that lacks a charging jack) or simply leave it on the track with power set to 12 volts or higher. The least desirable method would be to remove the battery and charge it externally.
Removing the cab of an engine unnecessarily courts errors that could, in turn, cause problems.
If the engine has a battery jack, can I make a jumper from an external charger to the engine to recharge without damaging the electronics?
I don't see why not.
Finally, can a lead from the engine's battery jack to a meter be used to check the amount of charge left in a battery (with no track power applied)?
No, a meter needs a load on the battery in order to read its state of charge accurately. You need to measure a battery's remaining capacity using a battery meter or by placing a bulb across its terminals.
Regardless, the best test of a PS2 engine's battery's state of charge is to simply start it up making sounds, either conventionally or under DCS, turn of track power (not press Shut Down) and count how many seconds sounds persist. If sounds don't persist for 6-7 seconds, the battery should be charged.
