Why does a multimeter show a measured output of around 85 volts insteald of the rated 120 volts?
This is normal for the output of this device, as the output waveform is a modified sine wave. 81-85 VAC is the RMS valule of a 110 VAC sine wave, and you will read aound 85 to 95 volts when measuring with a conventional Average Responding Multimeter. Comparably, you would get the same measurement when measuring the RMS voltage of a standard electrical outlet.