After you have replaced the 9V battery of the Smoke 2.0, you must carry out a Smoke test to reset the battery display. Otherwise, the app will continue to display "low battery".

To carry out a smoke test, go to the settings of the Smoke 2.0 and click on Smoke Test. (see screenshot) 

Then press the test button on the Smoke 2.0.


elements App -> Settings (3 crossbars at the top left) -> Elements -> Smoke 2.0 -> Smoke Test -> Press the test button on the Smoke 2.0.