Battery life.

Estimate runtime from capacity (mAh) + average current draw. Duty-cycle aware. Picks battery SKU on Manila shelf.

// input.md

battery capacity (mAh) active current (mA) — when device awake sleep current (µA) — when device idle duty cycle — % time awake

e.g. 5% = wakes 3 min every hour. 100% = always on. battery efficiency factor real batteries deliver less than rated mAh under load.

// result.md

estimated runtime — hours —

avg current —

effective capacity —

tips

Browse batteries → All parts →

// how_it_works.md

The formula

avg_current = (Iactive × duty) + (Isleep × (1 − duty))
runtime_hours = (capacity_mAh × efficiency) / avg_current_mA

Duty cycle — the big lever

An ESP32 pulls ~80 mA awake but <10 µA in deep sleep. A 2,400 mAh 18650 lasts 30 hours always-on, but 8+ months at 0.1% duty cycle (wake 3.6 sec every hour to send a sensor reading). Battery life is mostly a sleep-strategy problem.

Common gotchas

Voltage drop — devices cut out before battery fully empty (LiPo at 3.0V, alkaline at 0.9V). Real usable capacity is less than rated.
Boost converter overhead — boosting 3.7V → 5V costs ~15% efficiency.
Cold temperature — capacity drops 20–40% in cold. Heated PCB or insulation for outdoor projects.
Self-discharge — most LiPos lose 2–5% per month idle. Long-term sensors need lithium primary cells, not rechargeables.