Battery: kept back Your browser kept your battery level back. Firefox removed this API entirely in 2016, after researchers proved it could be used to track a visitor across websites without cookies, without consent. The API still exists in the specification. It was simply hidden — from you, and from any page that might ask after it.
Well, at least something positive from the shit I take for not sheepling my way through life using Chrome
I got this message and I'm on Chrome, on a laptop. I tested in the console on that site and was able to get the battery level though, so I'm pretty sure their check is just broken.