That's a good point. I did try to account for this by turning off everything I could: radio, MFD, A/C, lights, etc. The Scan Gauge did say I was pulling about 0.5 amps before I initiated the charging session. If we add 100W to the numbers that are going into the battery we get the following: 240V: 2025 / 2300 = 0.88 (12% loss) 120V: 1114 / 1533 = 0.726 (27% loss) 120V: 1114 / 1452 = 0.767 (23% loss) If we assume that it's more like 200W overhead, then the numbers are like so: 240V: 2125 / 2300 = 0.9239 (8% loss) 120V: 1214 / 1533 = 0.7919 (21% loss) 120V: 1214 / 1452 = 0.836 (16% loss) Keep in mind that there is overhead in an unattended charging session. We know the battery fans run, and we know that the 12V battery gets a trickle charge. We just don't know how much. A safe bet is probably 50W to 100W.
what typically accounts for much of the higher effeciency of 240V charging is that the fixed W overhead is only for half the time of the 120V session. ie. 200W x 1.5 hours versus 200W x 3 hours = 300Wh which is 10% of a 3kWh session.