The Ember Mug and Ember Mug² were built with the intention of pouring in freshly brewed coffee, hot tea, or hot liquids in general. This is how we always recommend using your Ember.
If a user pours in a drink hotter than their desired temperature, Ember's battery won’t be needed until their drink reaches the desired temperature. Once at the preferred temperature, the heaters in the Ember will turn on to regulate the temperature. This will allow you to also get the best battery life possible.