HTML5 seems to have introduced a new way to track innocuous website visitors on mobile devices such as laptops, mobile phones, and tablets – no cookies required! The level of detail provided includes 16 decimal digits – a double – on your battery health, which allows a website to get a pretty accurate and unique device profile. That means a way to track you!
There's no magic potion against this yet, other than to use Tor (which is a bit slower and doesn't support the battery life API for that reason). Then again, if you have no problem with cookies, would you really care?