Eighteen months ago we began gathering data on battery performance from our Android app – the metrics available on Android include charge level, voltage and battery temperature. These are relevant to our mission to understand and map the world’s wireless networks, since poor signal can lead to increased battery consumption.
After 6 months of data collection, we chanced on an unexpected relationship. Aggregating daily battery temperature readings to city level revealed a strong correlation with historic outdoor air temperature. With a mathematical transformation, the average battery temperature across a group of phones gives the outdoor air temperature.