It is all about the VA needed from the generator.
-DC output 14.4v x 55 amps = 792w
--Converter efficiency, say 88% so input watts = 900w
--WFCO PF is 0.7 (as reported by those with Kill-A-Watts) so that means VA needed is 1286. Which is why a "1000w" gen can't run a 55 amper of any brand, never mind a WFCO.
BTW my PowerMax 55 amper on my Kill-A-Watt shows PF 0.70 too, and with Honda at 126v unloaded, shows 124.7v, 11.06a, VA 1383, 980w with output of 56.8a, and set at 14.8v with battery rising through 13.7
---time2roll doesn't mind a slower charge than I can stand for :)
A 35 amper on 220AH takes about 3 hours to do a 50-90, while a 70 amper takes about 2 hours. (A 55 amper takes about 2.3 hours.) So I prefer the 70 amper to save an hour of gen time. But that means a bigger generator of course.