What’s the lifespan of a device (battery)?

The lifespan of a device is determined by the lifespan of its battery. As long as the battery is OK, the device can work fine.

Generally, the lifespan of a lithium battery is 2~3 years. After that, the performance of a lithium battery will begin to degrade gradually. But it can still work. Some Druid’s devices have been working for over 6 years now.