Radio runs on 9vdc...wondering if I power with 12vdc is 3vdc extra

Radio runs on 9vdc...wondering if I power with 12vdc is 3vdc extra

This radio runs on 9vdc. Would like to power with 12vdc in my rig by adding a jack to this unit. I went ahead and tested (hooked up) 12vdc to battery terminals and unit works….but for how long?? Do I need to limit current and voltage with a resistor or?? Thanks in advance.

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