DC voltage range for AC1750 WiFi cable modem/router

I would say that only a few volts either way since the router's ciruits are design for 12 volts dc too low the firmware could be damage or hardware and too high you could burn out parts in the router. You could run the router off a 12 volt battery with a fuse inline to protect the wiring from the battery remember a 12 volt battery charges at the mid 14 volt range depend ing on the battery type.