Yes, Ember Mugs are safe to keep on the charger when not in use. When the battery is fully charged, the charging is shut off automatically, so no battery damage will occur. Ember Mugs also have "maintenance charging", which means that if left on the coaster for months on end, the battery is periodically topped off because the battery slowly self-discharges.
If you are keeping your beverage hot while using the coaster, it can maintain your perfect temperature all day!* When Ember is on the charging coaster the battery will stay at a constant level and will not charge any higher until your Ember is empty or is powered off.
* The Ember has a 2 hour inactivity auto shutoff feature. Picking the Ember up to move the accelerometer will reset the 2 hour timer.
Once your Ember Mug has an empty battery, place the mug on the charging coaster for approximately 2 hours for a full charge. Once the LED turns green your Ember is 100% charged.
We are happy to say that the Charging Coaster² is compatible with all first and second generation Ember Mugs. In fact, the Charging Coaster² can also be used with the first and second generation Ember Travel Mugs as well.