Friend of mine  wanted really big power bank for his camping. So I made one. I bought brand new Xiaomi Mi 18W Fast Charge Power Bank 10000mAh and took it apart. After removing original cell, whole powerbank was cut by hacksaw. Cutted part nicely fits to 3D printed enclosure. With help of my trusty spot welder I made 1S30P from recycled 3.1Ah Li-Ion cells. Resulting battery is 3.6V/93Ah (330Wh) nominal. It will take some time to charge.. 🙂 For faster charging there is XT60 connector embedded in the case.