As per the comments, this was pretty common back in the old portable CD player days. It's usually just an exposed section of the battery casing (which is connected to the negative terminal), and there is an extra contact terminal in the battery compartment. It's basically just a really cheap and easy way to distinguish a rechargeable battery from a regular alkaline. I'm sure there are better ways of detecting the difference but this is old school, and cheap
If you watch dave's review of the agilent OLED multimeter, you'll see it dedicated an entire minute (or 3?) to determine what kind of battery is installed before charging
I find HaD is full of sheeple. Article says Philips is doing something dastardly so it must be true... Half the comments are "BURN PHILIPS ALIVE" while the other half is "um, its a legitimate design feature/necessity".