There are WFCOs that work according to spec. Like others, it took a lot of measuring to figure why my batteries were taking such a beating, and that my WFCO was not meeting spec.
I got my WFCO (8735) to go into bulk mode once. The second time it should have gone into bulk mode, it blew the 30 amp battery fuse without me noticing. The WFCO I had would also never go into trickle mode - I tried everything to coax it over a 4 week period, including dumping every parasite load. I learned to disconnect my battery while at home to prevent boiling water away.
Replaced it with a Progressive Dynamics 4135 converter/power center (alleged drop-in replacement for WFCO 8735). Except for being 1/2" narrower, and not having a 40 amp reverse polarity fuse, it was a true drop-in. The PD uses all 3 modes appropriately, and will hold bulk mode to about 90% for faster recharging. It does make some barely audible squeals (from the capacitors) when under heavy load. The fan is much quieter, and comes on sooner, than the WFCO fan. The fan will cycle itself as needed. I am very happy with the PD.
2014 Rockwood A122 A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time