range extender

Short definition from Wiktionary

Noun

1. 1
   A fuel-based auxiliary power unit that extends the range of a battery electric vehicle by driving an electric generator that charges the vehicle's battery.
2. 2
   A device which extends a signal beyond its normal limit.
3. 3
   A device which expands coverage available to a wireless network with a new coverage area, which can be connected to the primary network node via a wireless backhaul or a wired one, depending on device.