I have a few Sonoff SNZB-04 contact sensors installed that have been working for about 3 months.
The battery levels all show 100% full after this long.
Does the battery info not report properly for these devices?
I have a few Thirdreality contacts where the battery levels report just fine.
I installed mine in February and they all say 100%.
EDIT: I just realized that I was having issues with one of them and did see the battery level drop to 80%, at which point I replaced the battery, so maybe….
Also, they do seem slower to report than the Linkind contact sensors, which are my current favorite for being fast and reliable. I have the Sonoff setup on shower and bathroom doors to keep motion activated lights from turning off, which has worked very well to improve my families satisfaction with the automation.