My idea is a third-party back cover for mobile phones with non-replaceable batteries. A phone repair shop can replace the original back cover with the new one. That new back cover has an openable battery compartment, thus the battery is now user-replaceable. It connects the replaceable battery to the internal battery pins. (If parts of explanation is anyhow unclear, please ask for clarification in a comment.) Of course, there are also *battery cases*, but they can not be combined with other cases such as a phone case which allows the phone to stand in a viewing angle on a flat surface.