While the tiny built-in thermometers' main job is to prevent smartphones from dangerously overheating, the battery temperatures can also tell a story about the environment around them, the researchers said.
Crowdsourcing hundreds of thousands of smartphone temperature readings from phones running the popular Android app known as OpenSignal, the team estimated daily average temperatures for eight major cities around the world and found they could calculate air temperatures to within 2.7 degrees Fahrenheit of the actual value.
The method could one day make predictions possible at a much finer scale of time and space than is currently feasible, they said.
"The ultimate end is to be able to do things we've never been able to do before in meteorology and give those really short-term and localized predictions," James Robinson, co-founder of London-based app developer OpenSignal that discovered the method, said.
"In London you can go from bright and sunny to cloudy in just a matter of minutes. We'd hope someone would be able to decide when to leave their office to get the best weather for their lunch break."
The OpenSignal app collects information voluntarily sent from users' phones to build accurate maps of cellphone coverage and WiFi access points, but can also report data such as battery temperature.
The work was published in Geophysical Research Letters, a journal of the American Geophysical Union in Washington.