Exactly. From a purely practical standpoint, as an owner, what happens to the vehicle warranty if you add an aftermarket charge coil? You can kiss the warranty goodbye unless the car maker engineers the modification and installs it through a dealership. That includes the warranty on the battery itself, a hugely expensive replacement item. Regardless of the cause of a problem, any aftermarket modification will be blamed, and you, the owner, will be expected to pay.
With 8 year or 100K mile battery warranty, I wouldn’t want to tinker..