Whereas some size change is perfectly normal, it should not be overly pronounced. If so, replace the battery immediately. A bulging coin battery may lead to device malfunction and even short-circuiting.
Operating times may vary depending on the conditions in which you use your hearing aid. The most common cause is not letting it breathe after you take off the seal. Ensure at least 60 seconds of air flow before inserting it into the hearing aid.
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.