The ApexZ portable particle counter has the industries longest battery life. As we all know over time batteries begin to lose their efficiency, The ApexZ batteries have a sleep mode feature to reduce self discharge if the lithium-ion battery fully reaches 0% the cell could be permanently damaged. This feature prolongs the batteries life. If the battery is removed from the instrument and stored the battery will enter sleep mode. Which provides a minimum of 6 months shelf life, when stored at 20℃. To bring the battery pack out of sleep mode simply insert it into the ApexZ and apply power or put the battery pack on the charger.  Packs should never be allowed to discharge to zero capacity in storage. If you have any further question send us a live chat message on the bottom right of your screen.