Yeah, unless you specifically need to run something on 110 volts AC, there's not a lot of benefit to a traditional UPS.
Since the radios will run off 12 volts, you can make a pretty good system with a solar panel, charge controller and a battery.
UPS systems have a bit of efficiency loss to them. They have to take 110vac, convert it to direct current at the appropriate voltage for the battery pack, then convert it back to 110vac, then your scanner power supply converts it back to DC again. That generates some heat, some losses in the conversion, and all that reduces your battery run time.
A small solar panel and charge controller will easily keep a 12 volt battery topped off and depending on the size of your battery, run a whole lot longer than a consumer UPS will.