It is important to insert batteries properly into your SportEAR devices. Always match the plus (+) side of the battery with the plus (+) side of the compartment door. Most zinc air cell batteries have the plus sign marked on the protective tape. Once the tape is removed, it’s easy to forget which is the plus and the negative. When inserted properly the battery door should close very easily and the unit will work. If inserted improperly, the door will be very difficult to close and the unit will not work. SportEAR utilizes a #10 battery on In-the-Ear and Open Fit/Micro Behind the Ear units. The X-treme Head Muffs use an “AAA” size battery. Both of these batteries can be found at most retail outlets. Occasionally, it is possible to buy a bad battery, so remember to buy extra batteries when purchasing your SportEAR products.