WFCO-8955PEC unusual charging behaviour - is this normal?

I don't know if the WFCO is a pos and I'm not sure what converter was in our 5er but it died after 8 years. While is was functioning I had to add water every two weeks. I replaced it with 55 amp PD and watering went down to ever 6 weeks. The batteries were of unknown age as the 5er was 6 years old when purchased. The following year I replaced both batteries and in 5 years I have only added water twice. We are fulltime and usually on full hookups.