The Battery Thermokruzhkus MugĀ is a classic blackĀ ceramic mug with a white outline of a batteryĀ indicator on it. Pour in your hot liquid ā anything over 96.8F (36C) ā and watch the green cells within the battery light up. As your beverage cools the battery will fade into emptiness, reminding you that you need a refill. The mug isĀ availableĀ atĀ ThinkGeek for $14.99.