Others may prove me wrong but I think your battery monitor is a simple voltage monitor. I found the stock monitor to be grossly misleading. When it reads 2/3, you are almost dead for any useful purposes. (at least with my stock monitor). So I bought a simple Voltminder and hooked it into the buss to get a more accurate read. I found that, by the time my stock monitor showed 2/3, the actual charge was getting down around 50 to 60%; which means virtually nothing left; about 12.1 to 12.2 volts. You should never take your battery down below 50%. So, when I start seeing 12.3 volts or so, on comes the generator as you've already used at least half of your available power, while your stock monitor still says 3/3. I also like the Voltminder because it tells me the rate at which my WFCO is charging when I am running the generator. (We dry camp almost exclusively). There are more sophisticated devices out there for monitoring that give you even more information but I didn't want to spend that much. Some other members have gone that route and could tell you about that.
2012 F150 FX4 Ecoboost, 2016 Surveyor 274BHS
2003 Yamaha FJR1300, Demco Premiere Slider
1969 John Deere 1020, 1940 Ford 9N, 1948 Ford 8N
Jonsered 535, Can of WD-40, Duct Tape
Red Green coffee mugs