See these tips for extending battery lifespan Batteries - Maximizing Performance - Apple
Store it half-charged when you store it long term.
If you want to store your device long term, two key factors
will affect the overall health of your battery: the environmental
temperature and the percentage of charge on the battery when it’s
powered down for storage. Therefore, we recommend the following:
- Do not fully charge or fully discharge your device’s battery
- — charge it to around 50%. If you store a device when its battery is
- fully discharged, the battery could fall into a deep discharge state,
- which renders it incapable of holding a charge. Conversely, if you store
- it fully charged for an extended period of time, the battery may lose
- some capacity, leading to shorter battery life.
- Power down the device to avoid additional battery use.
- Place your device in a cool, moisture-free environment that’s less than 90° F (32° C).
- If you plan to store your device for longer than six months, charge it to 50% every six months.
Depending on how long you store your device, it may be in a
low-battery state when you remove it from long-term storage. After it’s
removed from storage, it may require 20 minutes of charging with the
original adapter before you can use it.
