A battery is an active component. Once you have charged the battery, and the application is not used, the battery will still loose some of its energy. This is called the self discharge effect or charge retention. The loss of capacity is presented in the curve below.
Storage curve under construction
The self discharge effect is influenced by tow major parameters:
The ambient temperature of the battery
The humidity
If the temperature is high and or the humidity is high, the battery will have a high self discharge. That means that the process of loosing stored energy is going faster. In contrary the lower the temperature and or the humidity will have a positive impact on the loss of energy. If products need to be stored for a longer period of time it is recommended to store at temperatures below room temperature and humidity's lower than 65%.