iPhone's "internal charger" not working

My mom's old iPhone 12 Pro Max's battery life is at 74% so I scheduled an appointment to get the battery replaced. It is important to say that there are no Apple Store in my city and no nearby for 6 hour drive. The appointment was made through the Apple Support app with a licensed Apple distributor. The issue is that when my mom took the iPhone to the store, they told her that it would not be possible to swap the battery since the "internal charger is damaged and no longer working". She did not receive anything in writing. But it is strange to me because her phone works just fine, it's just a matter that we would like to get the battery replaced. Can I get any more information about this "internal charger"? To me this sounds really sketchy. Thank you for your time.