I made a mistake and connected my Airpods with bluetooth scan and add device from my computer and when I tried to use them the left ear was without power.

It took we awhile to track down the problem, the left ear wouldn’t disconnect from my Macbook Pro, the image is from when both Airpods where in the case.

The fix was: put both in case and use case button to reset both (hold it down until if flashes white).  You will have to reconnect the Airpods to your devices.