The battery devices state Up to 5 years and that this may vary based on the default settings, usage, frequency of firmware updates and the environment its placed in.
For example if the Temperature/Humidity sensor was placed where temperature fluctuation were happening frequently this would increase the number of reports it sends and therefore increase the battery usage when compared to one that is reporting less frequently.
For example if the Temperature/Humidity sensor was placed where temperature fluctuation were happening frequently this would increase the number of reports it sends and therefore increase the battery usage when compared to one that is reporting less frequently.