A status of a battery operated infuser may be detected by measuring a controlled input parameter. The measurement may be used to determine a magnitude of the input parameter and a parameter of the control. For example, control of power input to a motor may be by pulse density modulation. An integral of current over time may serve as a measure of current magnitude and pulse density. The result of the integral may be used to determine the status of the injector. The status may include normal functions for example start of pumping and/or malfunctions such as occlusion or drive disengagement.