need help building a custom power regulator for my Nintendo Gamecube portable project

I'm building a custom Nintendo Gamecube handheld portable. I want to use a 7.2v 4500mA Lipo battery. I have found out that the gamecube mobo needs three different voltages. those voltages being... 1.9v at 6600mA max, 3.3v at 800mA max, and 5v at 350mA max. I calculated that the gamecube would consume 2270mA at 100% efficiency (which we all know is almost impossable). I would like to know how many mA the system would consume at say 55% efficiency, because I haven't found the math formula to figure it out. I would be very thankful if anyone can help me out.

Efficiency ε = Pout/Pin. Transposing, Pin = Pout/ε

Power P = E*I,

so, Ein*Iin = (Eout*Iout)/ε.

So if you have a Switcher to convert 7.2V to 1.9V that is 60% efficient,

then Iin = (Eout*Iout)/(ε*Ein) = (1.9*6.6)/(0.6*7.2) = 12.54/4.32 = 2.9 A.