Never show Battery OK

The battery available power is not only dependent on temperature and current voltage ( which is already incorporated).
Sometimes batteries “crash” from , what is considered OK, to unusable on a short time.

It’s OK to warn user that, based on current conditions, the battery should be replaced as that is prudent. But really It depends on the critically of the application and the ease of replacement. For example if monitoring the temperature of the basement( just because it’s nice to know when it’s cold ) with a ruuvi on top of a bookcase (easily accessible) many users would wait until the battery is completely depleted before replacement.

Telling the user that the battery is OK gives a false sense of security.