These apps don’t show the actual value at the time. Merely approximate and round up/down values.
The
Watch Juice app reports battery percentage in multiples of 5% on the Apple Watch due to limitations in
watchOS. Specifically, third-party apps like Watch Juice do not have access to the exact, real-time battery percentage of the Apple Watch due to Apple’s restrictions on data precision for battery information. Instead, they can only retrieve battery data in increments, often rounded to the nearest 5%.
This is likely done to reduce the power consumption associated with constantly querying exact battery levels and to align with Apple's privacy and security policies that limit the level of system data available to third-party developers. Apple’s own system apps, like the built-in Battery widget, have access to more precise battery data, but this isn’t extended to third-party apps through the current public APIs.