Right now I use my PW with WiFi on only when reading to sync with my KFHD7-32. I use light level 22 of 24 and read about 30 to 60 minutes per day.
I get 11 days to the 15% warning screen.
Reading times for many folks here seem to vary from 3 days to 30 days. Our reading habits definitely determine the reading time. They are all over the map.