if a user visits a website in Chrome’s private browsing mode using a VPN, the website should not be able to link them to a subsequent visit with private browsing and the VPN off. But the researchers warn that that may no longer work: “Users who try to revisit a website with a new identity may use browsers’ private mode or clear cookies and other client side identifiers. When consecutive visits are made within a short interval, the website can link users’ new and old identities by exploiting battery level and charge/discharge times. The website can then reinstantiate users’ cookies and other client side identifiers, a method known as respawning.”

Worse still, on some platforms, the researchers found that it is possible to determine the maximum battery capacity of the device with enough queries, creating a semi-permanent metric to compare devices.