No reason you can't do both. Here is a link for a "how to". It references the Bachmann Big hauler, but the priciple is the same for any electric loco.
http://members.shaw.ca/sask.rail/construction/lsbuild/460mods.html
The Dixie D Short Line "Lux Lucet In Tenebris Nihil Igitur Mors Est Ad Nos 2001"
It is certainly possible to have a combination of both.
Doing so does complicate the wiring inside the loco.
You will still have to maintain track conductivity and cleanliness. Which sort of defeats the purpose of having batteries. It has been my experience, that eventually the hybrid idea is abandoned and the locos run exclusively on battery power.
If you would care to give us an idea of what sorts of locos you intend using, and the method of operation you have in mind, more specific information will come from the many battery users who frequent this forum.
Best wishes,Tony Walsham (Remote Control Systems) http://www.rcs-rc.comModern technology. Old fashioned reliability.
Please excuse if already fully covered. Just starting out in this posting process.
What has been/is being done re combination of electrified track power and on board batteries?
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