I leave our Avenger plugged in all the time as well, and the WFCO has never boiled our battery dry either... in fact, the only time I've ever had to add any water was when we brought the camper home when we purchased it. I usually check the battery once a month, on average, or whenever I think about it, which is probably even more frequently, because I've read all the WFCO horror stories on here. But I have had no issues... maybe I got a good one?
Brian & Becky
2018 Avenger ATI 27RBS
Weber Q2000, Blackstone 22", and a whole herd of flamingoes