Magic Color Changing Porcelain Mug. When you put the hot water into the mug, the "color of the battery" will change gradually.. Before - r After. "Magic" you uneducated . It's because they're thermosensitive Magic Color Changing Porcelain Mug When you put the hot water into mug "color of battery" will change gradually Before - r After "Magic" uneducated It's because they're thermosensitive