Flux:
Well the 90 % it is not optimistic if the generator produces voltages about 3 to 5 times greater than the battery bank.
Normally, if one can measure the internal resistance of the generator and the external load is at least 9 times higher impedance than the generator's then one can calculate the power transfer and at the same time define what voltage level is needed to attain the % efficiency.
85 % efficiency is not difficult to attain, let's say a 1 KW generator with a peak voltage of 250 volts which represents 4 amps output.
Let's say the 10 % is lost in the generator or 100 watts which makes 100 watts / 4 amps= 25 volts drop internally in the generator and 225 volts going out at 4 amps rate, let say that the converter takes this 900 watts ( 225 volts @ 4 amps) and converts it to any desired voltage, like a 48 volts bank ( charging a 56 volts level with a current transfer of (225 / 56 ) * 4 amps = 16.07 Amps.
In addition let's say that this convert has an efficiency of 94 %, instead or 16.07 amps the current would be 16.07 * 0.94 = 15.1 amps for a total wattage of 15.1 * 56 = 845.6 watts
Generated power = 1000 watts
Delivery power = 845.6 watts
Over-all efficiency = 84.56 %
IN ADDITION this generator can start producing energy at a much lower wind regime, like at 80 volts, without boosting if the controller is well done with MPPT capabilities.
I have worked some 10 and 20 KW Wind Mills that produced around 87+ % efficiency with generators producing much higher voltage, charging high voltage battery banks.
Nando