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. - OpenSignal, How phone batteries measure the weather

Pretty impressive, all all the graphs are interactive. The find isn’t mind blowning, its known that batteries do discharge energy more quickly in cold weather.