Your Android phone's battery life could allow it to be tracked across different sites

A feature belonging to the HTML5 Battery Status API allows a website to know how much battery life is remaining on a device being used to visit it. The feature reveals battery life remaining for devices using the Chrome, Firefox or the Opera browsers. Among the data revealed by the API includes how many seconds remain until the battery has completely discharged, and the percentage of battery life remaining.

Once you've computed all of that information about battery life, the data can help determine the capacity of the cell being used on a specific device visiting a website or web-app. Once all of this information is discovered, certain patterns will emerge. The patterns can be used to track devices across different sites. Once you know how fast a certain phone is losing its charge, or gaining power, you can track how often a specific device has visited a certain website with a fairly high degree of accuracy.
 

Because information is updated every thirty seconds, there is a limited time that a device can be tracked. Still, half a minute appears to be enough time to obtain the necessary information allowing you to compare the battery-centric metrics of different devices, looking for a match. And once a match is achieved, other pieces of the puzzle start falling into place.

source: TheLeakingBattery via BGR