What you'd need is a DC adapter for USB. If you have one that has USB ports already, such as for your smart phone or tablet, you could use it with the USB cable that came with the scanner. Or, you could get an extra cable for mobile use, and leave the original at home.
I ordered this item. It has a cable, with the correct end for the scanner, plus two additional USB ports for other devices.
It's nice being able to power it with the USB cable and 12 volt.
I recently built a go box consisting of a Kenwood TM-V71A. It runs off of a LifePO4 battery, a DC power supply, or solar. When I built my box I put in a pair of USB connectors primarily for charging phones, it will also power the 436. I take my batteries out of it if using it to power the 436 to failsafe any oops.
Why? There is no issue running the scanner off USB power with batteries installed. That's how most people run the scanner in a base or mobile role. You're more likely to have an oops running the scanner with no batteries and rebooting unnecessarily because the USB cable got bumped.
The only caveat is that some USB voltage converters generate RFI. If you notice noise or degraded reception when running on USB power, you may need to use a different USB port or voltage converter.