Battery life and power budgets

Battery life — describe one cycle of the device: the active states with their current and duration (radio burst, sensor read…), the sleep current that fills the rest of the period, and how often it wakes. The average current is ΣI·t/T; life = capacity × usable fraction ÷ (average battery current + self-discharge). The converter-efficiency figure scales the battery current for a regulator or boost converter (100% if the device runs straight from the cell). The bar shows which states use the charge — usually the radio, or the sleep current if wake-ups are rare. Presets are typical datasheet figures for ESP32, ESP8266, nRF52, LoRa, AVR, and common peripherals: measure your board, because regulators, LEDs, and pull-ups often dominate sleep current. A state’s Every column runs it once every that many seconds instead of every cycle — an hourly sync or a daily over-the-air check — so it counts at its own rate. The regulator’s quiescent current is drawn from the battery all the time, on top of the load; the temperature scales the usable capacity (approximate figures per chemistry: alkaline cells lose ~40% at 0 °C, lithium cells much less). The daily energy budget lists mAh and mWh per day for each state, sleep, converter loss, quiescent current, and self-discharge.

Chemistries — nominal, full, and cutoff voltage, typical capacity, self-discharge, cycle life, and practical notes for Li-ion, LiPo, LiFePO4, alkaline, NiMH, coin cells, lithium AA, and lead-acid.

Pack builder — series cells add voltage, parallel strings add capacity: voltage, capacity, energy in Wh, typical continuous current, and mass. Series lithium packs need a BMS. To design a real pack — cell presets, size, BMS, fuse, and nickel-strip links — use the battery pack builder.

Charge time — lithium chemistries charge at constant current to about 80%, then the constant-voltage phase tapers the current; NiMH and lead-acid are estimated with a charge efficiency. Treat the result as an estimate.

Solar sizing — panel watts = daily Wh ÷ (peak sun hours × system efficiency) × margin; battery Wh = daily Wh × days of autonomy ÷ allowed depth of discharge. Convert an average device current to Wh per day with the panel on the right.