Language: EN

Battery life calculator

Most battery-powered devices sleep almost all the time and wake up briefly to measure, compute or send. Enter the sleep current and each event, and the calculator gives the average current, the battery life and how much each part costs.

tTI_sleepI_eventI

Battery and sleep

Events

Each event is a current for a duration, repeated at an interval. For example a sensor reading, a radio packet or a flash write.

    Results

    Battery life
    –
    Average current
    – µA
    PartAdds on averageShare

    How it’s calculated

    The sleep current runs all the time. Each event adds the current above sleep for the fraction of time it runs. The battery life is the usable capacity divided by the average current.

    I_avg = I_sleep + Σ (I_event − I_sleep) · t_event / T_event
life  = capacity · usable / I_avg

    Keep its limits in mind.

    • Keep a margin. A battery gives less in the cold, at high peak currents and as it ages. A usable capacity of 70–80 % is a reasonable start.
    • Self-discharge isn’t included. It matters for devices meant to last months or years.
    • Enter currents as measured at the battery, so the regulator’s losses are already in them.
    • Events are taken as separate. If two often run at the same time, enter them as one event with their combined current.