Negative Value: The negative value your Leak Detectors report is a bug in the battery level algorithm. We'll be releasing a fix for it shortly.
Incorrect Values: As for the incorrect levels and minor deviations, our Leak Detectors use Lithium Thionyl Chloride batteries that have a very flat discharge curve.
A direct voltage measurement can't give you information about the capacity, so we have an algorithm that takes into account the voltage droop under load and the amount of activity in its lifetime. There is a small bug that exaggerates the impact of some events.
To fix this issue please make sure your iOS app is updated to version 2.15 or higher.