Thomas D. Erb
I'm not familiar with this type of master - but if it is really voltage-sensitive you can also use a diode - each diode will subtract .7 volts from the power supply.
alkaline batteries nominal voltage is 1.5VDC so 3 in series would give you 4.5VDC.
If the master really draws 350ma - you would'nt get a lot of life -
A D cell battery will give you 12000-18000 mAh
12000/350=34.2857 to 18000/350=51.4286