speculation
@lunareclipseYou may already know this, but I wonder how much of this is people being confused by Android's rather terrible IMO UX for battery usage. It doesn't show how much percent of the phone's battery an app used, it shows the percent of the decrease it thinks an app is responsible for. (your phone battery dropped 10% over 10 hours, and it thinks the app used 50% of that). So this number naturally depends on how much or little every other app is using, even if the actual battery usage stays the same.
github.com/binwiederhier/ntfy-android/issues/90#issuecomment-2389466845
shows that pretty clearly. Looks like ntfy used ~10% of actual battery over 12 hours.