To replace 3 AAA Batteries with a power lead from 12v-4.5v

Buy offer Details

I wish to remove the 3 AAA batteries my units is using for power combined 4.5 volts
I would then like a product I can wire to a 12v power supply so
I will need a product developing that replaces theses batteries
so I can swop out the batteries
Insert the developed device which now will have a wire coming out of my units with the required 12v-4.5v reduction
I hope this is clear and enough information
And I’m looking forward to receiving a response from any interested parties who have the necessary skills and experience to develop a long standing business relationship