dean...for re #5, rcx version 1.0 had dc jack on them but newer one removed this although I think someone said the traces were still on the pcb inside if you're or could find an electronic person :-)
bruce...what is this with a battery powered train?? ugh remind me why I lost interest in playmobil....hmmmmm..... is lego still going to release the track powered trains in parallel to the battery one or ? (I mean, how fast is the battery going to run down if you try run one engine with six heavy wagons at a rail show? heh)
oh yeah dean just one little hint on used trains just in case, there were two different track systems. the older one was like this:
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and was used for dummy & 'battery boxcar' powered 4.5V trains. and you added what would look like a double third rail to run wall powered 12V trains like as seen here:
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just thought I would share that as a FYI. then again the info below is optional as I'm thinking you're only going to buy retail tracks which is
100% new style........ the old track don't match up with new tracks directly although you could try line up two straight tracks with each other and mind the bumps as the wagons crosses the different tracks. the old and new are generally the same gauge although the new tracks seem a little bit narrower than old one so don't be surprised if newer rail axles on old track has a bit of space for side-to-side rocking, the old switches would still work fine as long as they're not taken at high speed
*grins*