Adding to this,
sensorBatteryNeedsCharging set be called when the battery is actually completely depleted, to the point the sensor can no longer stream.
Thanks to the internal low-power processor, the sensor is able to connect and inform your app that its battery is depleted via this
sensorBatteryNeedsCharging callback, even if the battery is already completely dead when you plug it in.
sensorDidLeaveLowPowerMode actually doesn't return a boolean, but is only called when you are leaving the low power sleep state, and are transitioning to the full operational mode.