This amazing mug starts off black with an empty battery on it. As you pour in your hot liquid you see the battery glow green where the liquid touches it !
Then as you drink your coffee or tea the battery will adjust to where the liquid sits. When the cup either cools down or you finish the contents, the battery will be empty again.
Its a great way to know when you need a refill. A great gift for anyone who loves their coffee!
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