Effect of Battery Charge on Energy Consumption

The power consumption of a mobile device has been measured with a continuously repeated multimedia use case starting with a full battery charge until the battery empties. We have discovered a clear dependency between the charge level of the battery and the power consumption of the device. The origin of this finding is associated with the DC-DC conversion made between the battery and the components inside the mobile device. The practical consequence is that e.g. software developers optimizing the energy consumption of their code must be aware of this phenomenon since minor changes in the code may be easily shadowed by the found effect. We provide some advice how to avoid or alleviate the error caused by the battery charge level.