These are the top of the line batteries from Rayovac, with up to a 4 year shelf life and guaranteed freshness. Rayovac Proline are only sold through Audiologists and Hearing Aid Dispensers.According to Rayovac, Proline Advanced are the longest lasting battery and Rayovac is a leader in hearing technologies! Rayovac uses digital imaging and 104 quality checks to test every battery so we can ensure you receive a powerful consistent battery every time.