If this is the "Tongshi DAMB-R" radio
, the user's manual states a power consumption
of less than 1 Watt. You will be hard-pressed to find a 220V inverter
that will be efficient enough to compete with even a simple D-Cell battery charger
This radio has a power jack in the back, and it takes 6V at a peak draw of 0.3 Amps. I would get a 12V adaptor that puts out 6V, and use this instead of either the inverter or the batteries.
[Edit: I guess this is a different radio than the DAMB-R, which uses two AA cells. Still, an external DC power supply (if possible) would be my preferred way to go.]