These days injector behaviour at different voltages is well understood. The speed of opening and amount of fuel delivered vary with voltage. Corrections are made in fuelling calculations to account different performance for differnt voltages at the injector. If what the Megasquirt ECU understands is the voltage at the injector is different in reality, then it is likely fuelling calculations will be incorrect. This is why the battery voltage calibration needs to be correct in your Megasquirt ECU.