For my math, I use 4.15v × cell count × charge rate ×1.25 safety factor. But you are right, 5v gets you to the same place (25w per cell) WRT wattage.Ok thanks for the addition about the safety factor, will include that.
And yes i will use 4 parallel boards on the 2 chargers. So 8 lipo's in total.
The boards double the mAh's as you mentioned.
The calculation is for 1 psu, 1 charger, 2 channels and 4 lipo's. Should have made that clearer, sorry.
And in your rule of thumb you take 5 volts per cell? That is where the safety factor kicks in?