A 2.5 ohm dual coil is unlikely to provide a satisfactory vape from a 3.2v regulated battery. You'd be far better served with a single coil 2.5.
The deal with the dual coils is that they have a couple of high ohm coils wired in a parallel circuit. If you don't have the voltage to heat up one coil, having two isn't going to help. A 2.5 ohm dual coil has a couple of 5 ohm coils. 5 ohms is appropriate for 6 to 7.4v vaping, but not 3.7 and certainly not 3.2.
the eGo batt with a 2.5 ohm DC will only produce about 2 watts per coil. When the carto is freshly filled with juice, it will be even less and there sure won't be much vapor from either coil at under 2 watts.