Smart Battery Case QI charging behavior.

I QI charge my iPhone XS (inside Apple smart battery case) during the night. Sometimes, in the morning, the battery case HAS LOST charge (down to 40-50%), while the iphone gets a full charge. Sometimes my battery case gets a full charge but, my iphone battery gets DEPLETED. And, sometimes everything charges perfectly. In the instances of mal-charging the case is very warm. Lightning cable charging remains flawless, and corrects these situations when needed.

I have done the resets and have used 3 different QI chargers. This began after approx. 6 months of perfect charging. Strange.