Well *technically* a PWM mod is pulsing the battery at its full voltage potential. So, with a fully charged 4S pack (16.8v), and allowing for voltage sag under load, let's assume the pack can put, say, 14.2v across your .33ohm coil. In that case, each pulse is at over 43A (or right at about 20C for your 2.2ah pack, which is within its safety specifications), for a whopping 664 watts. In practice though, the actual results with PWM are a bit different. At a duty cycle of, say, 25%, the "effective," or RMS voltage would be around 7.1v (14.2v x SQRT(.25)) at 21.5A, or about 153 watts. In practice, the limits of your battery are with respect to time and wasted heat as well. So, even though each pulse is technically at the battery's full voltage, firing at 25% power for a relatively long period of time does not put more stress on your battery than firing at 80% power for a shorter period of time, even though it seems like it should.
