Battery life is usually the first constraint on a wireless IoT device. It is not a single number on a datasheet but the result of a budget: the current drawn in deep sleep, multiplied by most of the device’s life, plus the energy of each wake-up, reading and radio transmission, multiplied by how often they happen. Radio choice dominates the second term; a Wi-Fi connection costs far more per message than a LoRaWAN or BLE frame.
Real batteries complicate the arithmetic. Capacity falls in the cold, a coin cell cannot deliver large current pulses without a capacitor to help, and self-discharge sets a ceiling regardless of load. Designers therefore validate with measured current profiles and report battery voltage so the platform can schedule replacements. The IoT device types and constraints guide treats power as the defining constraint.
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