Powerbanks differ in the amount of energy they can store. Usually this capacity (in a colloquial sense) of the powerbanks is stated in the form of charge in mAh for effective advertising. From a physical point of view, shouldn't the energy that a powerbank can provide be of interest? For students, charging smartphones with power banks is commonplace--but the terms voltage, current, power, charge and energy are often not understood clearly. Since misunderstandings can also be expected on this subject, a more detailed analysis of the characteristics of powerbanks provides an opportunity for a context- and life-oriented physics education. In combination with microcontrollers such as the Arduino, simple, inexpensive computer-based experiments and measurements are possible. In this article we present a measurement circuit (see figure 1) for the Arduino, with which series of measurements on the characteristics of various powerbanks can be recorded and evaluated during discharge. Example measurements of various powerbanks are shown and discussed.