Here is a compact power bank that you can carry with your keys and use anywhere to keep your phone charged. Tau is the size of a keyfob and has integrated connectors to work with USB-C, MicroUSB and Lightning devices. Its dock keeps the power bank charged all the time.
You can install the charging case on the wall using a double-sided tape. The battery has 1400mAh capacity to add over 8 hours of talk time to your phone.[where to get it]