Panasonic hearing aid batteries, or zinc air batteries, react with air. As soon as you pull off the seal, the battery will be able to release energy. Be sure to let the battery breathe for a few minutes before inserting it into your device.
Once a seal is peeled off, the battery starts ‘breathing’ and therefore gives of energy, even if it’s not used in a hearing aid. The battery therefore won’t last until the expiry date if the seal is removed.