https://www.theregister.co.uk/2020/01/13/apple_launches_battery_case_replacement_program_over_charging_issues/

Apple has announced yet another replacement programme — this time for several models of its pricey Smart Battery cases.

According to a post on Apple's website, some cases will fail to charge when connected to the mains — or will charge intermittently. The flaw also prevents the battery case from discharging juice to the phone, which is pretty much the entire point of them.