According to Mooch, on a regulated MOD you take to account the amperage draw at the lowest battery voltage your mod can take and its given efficiency. it's not a direct draw as in a mech mod.
Wattage per Battery = Total Watts on mod screen / # of Batteries.
Mods Cut out voltage = Depends on your specific mod, varies from 3.0 to 3.2 Volts.
Mods Efficiency = Also dependant of your mod, varies from 80% to 95% on a god DNA.
Amp per Battery = Wattage per Battery / Mods Cut out voltage / Mods Efficiency
So lets say your build you run it at 100 watts.
on a dual battery mod would be 50 watts per battery.
I'll say your mods cut out voltage its 3.2 volts , with a 85% efficiency.
Amp per battery = 50 watts / 3.2 Volts / 0.85
Amp per battery = 18.3 Amps
so if you run a 20 amp rated battery you'll be running at 92% of its nominal amp load.
and if you run 25 amp rated battery you'll be running at 73% of its nominal amp load.
in either scenario, you should be ok, (as long as your mod its ok). at the end you won't have the best battery life that all.-