So it's a workaround for all the dead phones that can't charge because of U2 chip failure from non-Apple charger usage. Make and sell an external U2 chip-on-a-backpack to provide your phone with an externally chargeable battery. Way to spin that one Apple. Nice save.
The phone still uses it's own charging IC, this IC is most likely only used for charging the battery in the case and feeding battery charge data (from the Ti chip in the base of the battery) back via the lightning port.