You want high-discharge
batteries for those high-watt mods. Remember Volts X amps = watts. So the bigger the watts it can put out, the more amps the battery as to be able to put out (voltage is pretty much same for all in a mech, but variable in those mods). So high-watt-
mod = high-amp-battery.
And for theory/trivia/notes...use 4.2 volts for the voltage calc, or even use the low end at 3.5. Since Watts = Volts x amps....you can say that necessary amps = watts/volts (plus some overhead). So for a 70 watt mod, a battery would have to put out at least 70/3.5 + overhead which equals approximately 20 amps (so go higher, like 30 amps or more continuous discharge rating) due to overhead and also variable voltage and safety margin...
In reality, check the website and/or manufacturer's recommendations. Do research. Different mod circuits may have different characteristics. Then there's mechs.
The real trick is finding quality
batteries. IMR or better tech highly recommended.