IMPORTANT: These batteries are only designed to work with a PowerOne Pocket or Pen Charger. These DO NOT WORK with Oticon Hearing Aids or Z Power Chargers or with many build in hearing aid chargers. If you have not used this hearing aid battery in your device before, please check with your audiologist or device manufacturer. NiMH Rechargeable Batteries have significantly less capacity than a disposable. You may need more than one battery to last an entire day. Please purchase accordingly. These items are not returnable or refundable after opening!