A medical infusion pump and a method for logging a power source voltage of a medical infusion pump are disclosed. The medical pump may include a power source, a processor, and a voltage supervisor which responds if a voltage (VDD) drops to a response voltage level which is above a reset voltage level of the processor. When the voltage supervisor responds, the processor start logging the voltage (Vbat) of the power source in a memory, thus generating a voltage log. The memory maintains the logged data when the power supply by the power source is interrupted, thus enabling retrospective analysis of the voltage log.