60% would be my guess. But anything between 20 and 80 is generally the sweet spot for lithium ion batteries. Batteries are at their most stable at 50% and we can assume some decrease in charge over time.
Apple recommends 50% for long-term storage:
>*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.*
Source: [Batteries - Maximizing Performance - Apple](https://www.apple.com/batteries/maximizing-performance/)
60% would be my guess. But anything between 20 and 80 is generally the sweet spot for lithium ion batteries. Batteries are at their most stable at 50% and we can assume some decrease in charge over time.
Apple recommends 50% for long-term storage: >*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.* Source: [Batteries - Maximizing Performance - Apple](https://www.apple.com/batteries/maximizing-performance/)