Batteries discharge over time, and long time storage should be avoided. Please refer to the following FAQ on how to store batteries. 

If the battery has been stored over a long time you should carry out a battery load test to verify the battery initial state. Make sure to apply the instrument specific load, contact support@nortekgroup.com if you need more information. 

Lithium-ion (rechargeable):
Store in a dry place at a temperature preferably not exceeding 30°C. For long-term storage, keep the battery within a (30 ± 15) % state of charge. Do periodic checks to avoid complete discharge since this will harm the battery.