Instructions
To ensure a solid seal with the battery cap, there is a point while twisting the cap closed that the cap will feel like it has reached the end, please ensure that the cap gets a final 1/4th of an inch turn and the cap shows in full locked position. If the cap does not get to the full locked position it will not function.
You can see those positions on the battery case here:
https://photos.app.goo.gl/
Here are 2 videos to show the cap being fully closed into locking position:
https://photos.app.goo.gl/
https://photos.app.goo.gl/