Power, in watts, is equal to current times voltage. So at 2 amps with a 3.4volt battery you're looking at 6.8 watts. How do you get the current? Easy, too. Current = voltage divided by resistance. So, a 2.0 ohm atty running at 4.0 volts is drawing 2 amps. In this example, the wattage would be 2 amps times 4.0 volts, or 8 watts.