The Ember is 100% safe to keep on the charger when you are not using it. When the battery is fully charged, the charging is shut off automatically, so no battery damage will occur. The Ember Travel Mug has maintenance charging, which means that if the empty Ember is left on the Charging Coaster for months on end, the battery is periodically topped off because the battery slowly self-discharges.
Looking for answers? You've come to the right place.