IoT Power Budget Calculator

Sleep current is entered in microamps because deep-sleep draw on a modern MCU is typically only 1-10 uA, while active and TX current are entered directly in milliamps since sensing and radio draw is usually in the single or double digits of mA. The engine divides sleep current by 1000 internally so all three phases combine in consistent mA units before averaging — entering a value in the wrong unit for either field will throw the average current off by a factor of 1000.

Sleep time is whatever is left in the cycle period after subtracting wake time and TX duration: cyclePeriod minus wakeTime minus (txDuration converted from ms to seconds). If your wake time and TX duration together exceed the cycle period, sleep time is clamped to zero, meaning the device is effectively active for the entire cycle with no rest phase.

This model averages current draw over the full cycle, but it doesn't account for voltage sag or the higher effective internal resistance a cell exhibits during a brief current spike, like a LoRa or WiFi transmit burst. Coin cells such as a CR2032 are especially prone to this: their internal resistance rises as they age and under high-current pulses, which can shorten real-world life below what a simple time-weighted average predicts.

Self-discharge reduces the battery's usable capacity before the battery-life math runs: usable capacity equals rated capacity times (1 minus self-discharge percent). A lithium primary cell typically self-discharges only 1-3% per year, while alkaline cells can lose 5-10% per year, so choosing the wrong chemistry here will bias every downstream battery-life figure (hours, days, months, years) by roughly that same percentage.