This topic is one of the trickiest topics. There is no one size which fits all solution. The power requirements for the same device may vary depending upon how it is used by the sketch and how the circuit has been designed. Power source capacity is usually measured in terms of how much current can be supplied by a battery and for how long it can supply the current. Precise power consumption is an advanced electrical engineering topic; we will focus on learning how to determine approximately how many batteries we should use in our projects. Learning this should help you to become ready for the challenge of building standalone devices.
How many batteries will my device prototype need? How long will it run given x number of batteries attached to it? Let's try to understand the answers to these questions. The power source capacity is usually...