basic electronics question - series circuit
i have a device which normally uses a transformer rated at 2 amps outputting 5 volts. i want to put together a battery pack to power this device. it's easy enough to put together the batteries and get a 6 volt output, but i'm worried about burning out the device w/a 6-volt power source. i'm thinking putting a resistor in the circuit should be enough to lower the voltage to 5. if i remember my high school physics right, i'd need a resistor whose resistance is
r = (v1 - v0) / i = (6 - 5) / 2 = 1/2 ohm
...but this seems strange. 1/2 ohm?? my approach must be too naïve. can anybody point me in the right direction?