Portable wireless devices typically operate for long periods drawing only hundreds of nanoamps to tens of microamps of current, interrupted by short, power-intensive active modes requiring hundreds of milliamps or more. Testing these devices requires fast measurement sampling so that short-duration current spikes do not go undetected, giving a misleading representation of the power consumption of the device. This application note reviews methods for capturing the load current characteristics of a device or the voltage discharge profile of a battery.