In particular the ones designed to get around Sony's battery filter.
If you try and fit aftermarket batteries to some Sony's the camera detects the discreet ciruitry within them and a warning comes up telling you can't use it. To get around this the aftermarket people provide you with a lead that plugs into the back of the battery, then into your charging socket, so the camera now thinks it's an external power supply and it all works. Well, for a while at least.
I've been using one for months, but it's now fried my HC5 external supply function. I know it's the battery that's caused this as it emitted a crack, a little puff of smoke, and is now completely dead from a fullly charged condition. The external power function is now goosed, I can't power it up that way or use it to charge battteries on the camera.