It is best for the battery's health to ensure that the device is not stored for more than 2 weeks with an empty charge. When storing the device for a month or longer, it is best to charge the device fully and remove the pod and replace its cap before storage.
We also recommend storing your device on a scrap piece of paper (with the pod removed) vertically on the mouthpiece end - this will allow any e-juice that may have entered into the device to drain away.