Battery Life Calculator

Duty cycle is the fraction of time your circuit draws the average current you entered, so for a sensor node that wakes every 60 seconds for a 200ms reading, that's roughly 0.2/60 = 0.33% — set it close to that figure, not 100%. The calculator multiplies your average current by duty-cycle-percent/100 to get an effective current, so getting this number right matters more than almost any other input for a deep-sleep design; even small errors here compound directly into the runtime estimate.

They model two different loss mechanisms. Discharge efficiency accounts for the fact that a battery rarely delivers its full nameplate mAh under real load conditions — the engine multiplies rated capacity by this percentage first. Self-discharge then further reduces that usable capacity to reflect how much charge the battery loses just sitting unused before you ever draw from it, which is why NiMH cells (around 20%/month) need a much larger self-discharge value than lithium chemistries (2-3%/month) for an accurate long-shelf-life estimate.

The calculator doesn't model the Peukert effect, where pulling higher current from a battery reduces its usable capacity beyond what a flat efficiency percentage captures — so projects with current spikes well above your entered average (a radio transmit burst, a motor stall) will discharge the battery faster than the flat-average math here suggests. It also ignores temperature effects and the voltage sag/cutoff behavior specific to your chemistry near end of discharge, so treat the runtime figure as an optimistic upper bound rather than a guarantee.

Runtime (hours), along with its day and minute conversions, is usable capacity divided by the duty-cycle-adjusted effective current — a single continuous-discharge estimate. Days To Depletion is calculated separately from a daily energy consumption figure (effective current × 24 hours), so for steady, always-on-pattern loads the two numbers converge, but they're computed through slightly different paths in the engine and are provided as independent cross-checks on the same underlying runtime.