WMR918 Battery condition gauge

The batteries in my indoor barometer/temperature and humidity sensor have been get low for some time. The battery level went down to 80% and remained at this level for quite some considerable time.

Obviously, slowly as the battery discharged, the gauge should have indicated this, but it still remained at 80%.

It became obvious that a problem existed when the barometric pressure increased dramatically from 1019hpa to 1050hpa and then levelled out at this reading for four days!

It was then that I decided then to replace the batteries and the barometric pressure shot down to 1019hpa and the battery level went back to 100% charge.

Is there a way that you can check that this is working okay please as it seems that the battery level gauge may not be operating correctly with the sensor battery voltages as the cells slowly discharge.