If the current draw is significant you'll be generating quite a bit of heat dropping from 12 >5 with a linear regulator. A lower voltage battery will help, otherwise you'll need to think about heat sinking if you make it. A car adapter is where I'd start - it's cheap and usually delivers 500-1000 mA.
I googled power consumption and found that 2.5 watts is typical.
Watts = Volts x Amps
So 500 mA should do it and the car adapter is your friend.
Another spot I just checked spec'd start up at 1000, seeking at 500 and idle at 250 mA.