Dividing down 22.5 volts by 1.5V volt battery cells (AA, AAA, C, D) yields (15) batteries that would be in series.
This can be accomplished using (5) 3-cell AA holders in series:
http://www.digikey.com/product-detail/en...
A typical AA has 1500 mA * hours and would be able to supply 75 milliamps for 20 hours.
There is a formula for figuring this called "Ohm's Law"
It says the Voltage in a simple direct current loop equals the current in amps multiplied by the resistance in ohms. The answer in this case is 22.5 volts
Theoretically a 24 EMF battery with an internal resistance of 20 ohms would get it done quite handily. Realistically you will not find such a battery and would have no way of identifying it even if you did find one.
2 x 12 volt batteries in series
V = IR
= 0.075 x 300 = 22.5 ohms
