The hyG Ionic Toothbrush uses an integral lithium battery (coin shaped weighing 0.7g - non-replaceable), which will last 3-4 years of normal brushing. Plaque is difficult to remove because it has a positive polarity while teeth have a negative polarity. This opposite polarity naturally attracts plaque to your teeth. The metal plate on the hyG is held during use with a moistened finger and the bristles become negative charged. This breaks the ionic bond by temporarily reversing the polarity of tooth surfaces. As you brush, plaque molecules are actively repelled by your teeth and drawn to the negatively charged bristles. There is a built in battery tester to allow the battery to be tested once a month.