How this calculator works
Weight awake and sleep consumption by their time fractions, then divide usable charge by average current. Power inputs are converted to current using the battery voltage. Enter power at the battery terminals, including converter losses. Self-discharge and start-up surges are outside this constant-load estimate.
Formula
Iavg = (Ia ta + Is ts)/(ta + ts); I = P/V; t = Q x usable fraction / Iavg.
Worked example
A 2 Ah battery with 80% usable capacity and a steady 100 mA load lasts 16 hours. Alternating 100 mA for 1 second and 1 mA for 9 seconds averages 10.9 mA.
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Frequently asked questions
What does usable capacity mean?
It is the fraction you plan to consume before recharging. An 80% setting leaves a 20% reserve.
Which units should I use for consumption?
Each current or power field offers the matching unit selector; the initial units are mA and watts.
Will a sleeping sensor really last this long?
Battery self-discharge, regulator quiescent current, radio bursts and cold weather can shorten runtime.