The Battery Life Calculator (Hobby) estimates runtime for Arduino, ESP8266, and maker projects from battery capacity, average current draw, system efficiency, and usable capacity. Accurately models sleep/wake duty cycles and voltage regulator losses that dominate real-world IoT battery life.
1,600
mAh
58.82
mA
27.2
hours
1.13
days
1,600
mAh
58.82
mA
27.2
hours
1.13
days
Every maker project eventually confronts the battery life question: will this wireless sensor node last a week on two AA batteries, or three days? The gap between the theoretical calculation and actual field performance comes from three sources — current peaks during radio transmission that the average measurement misses, parasitic draws from voltage regulators and pull-up resistors, and battery capacity derating from operating voltage cutoff. The calculator for hobby battery life addresses all three through the average current, efficiency factor, and usable capacity percentage inputs.
Maker projects rarely draw constant current — they alternate between sleep modes (microamps to milliamps) and active modes (tens to hundreds of milliamps during sensor reads, computation, or radio transmission). The average current is the time-weighted mean:
I_avg = (I_sleep × t_sleep + I_active × t_active) / (t_sleep + t_active)
For an Arduino Uno with ESP8266 WiFi that sleeps at 15 mA total (no deep sleep) for 59 seconds, then wakes and transmits for 1 second drawing 120 mA: I_avg = (15 × 59 + 120 × 1) / 60 = (885 + 120) / 60 = 16.75 mA. Compare this to an Arduino Pro Mini with proper deep sleep at 0.015 mA for 59 seconds: I_avg = (0.015 × 59 + 120 × 1) / 60 = 2.0 mA — an 8× improvement in battery life from deep sleep implementation alone. Use this online calculator to compare scenarios. The Arduino current calculator helps estimate component-level current budgets.
Reference capacity values for batteries commonly used in maker projects:
Linear voltage regulators (LDO regulators like the commonly used AMS1117) waste energy as heat proportional to the voltage drop: efficiency = V_out / V_in. A 3.3V LDO running from a 5V USB supply: efficiency = 3.3/5.0 = 66% — meaning one-third of the battery current is dissipated as heat rather than powering your circuit. Switching regulators (buck converters) achieve 85–95% efficiency regardless of input-output voltage ratio. For battery-powered projects, always use a switching regulator when the voltage difference exceeds 0.5–1V. The 35% efficiency difference between a linear and switching regulator translates directly into 35% longer battery life. The Ohm's law calculator and maker electronics calculators provide complementary circuit design tools.
Most microcontrollers and sensors have a minimum operating voltage (typically 2.7–3.0V for 3.3V systems). A LiPo battery discharged from 4.2V (full) to 3.0V (minimum) uses approximately 85–90% of its nameplate capacity — the remaining 10–15% sits below the usable voltage threshold. For alkaline AA batteries powering a 3.3V circuit through a regulator with a 0.5V dropout, the cell becomes unusable at 3.8V (regulator input minimum), leaving approximately 30% of the AA's total charge unusable for this circuit. Understanding these voltage cutoffs allows accurate usable capacity percentages rather than assuming 100% utilization.
The base formula is: t = C × DoD / (I_draw / η), where C is battery capacity in mAh, DoD is depth of discharge as a fraction, I_draw is average current draw in mA, and η (eta) is converter efficiency as a fraction. The effective capacity is C × DoD (the usable portion). The adjusted current draw accounts for converter losses by dividing by efficiency. Life in days is simply life in hours divided by 24.
Results are theoretical estimates. Real battery life is typically 10–30% less due to temperature effects (cold reduces capacity), aging (capacity degrades with cycles), voltage sag under load, and peak current spikes. For mission-critical designs, apply a safety factor of 0.7–0.8 to the calculated runtime. For IoT projects, the calculated value is useful for comparing design alternatives even if absolute accuracy is limited.
Inputs
Results
An ESP32 sensor that wakes every 10 minutes, transmits for 500ms at ~100mA, and sleeps at 10µA averages about 1mA. A 2000mAh LiPo powers it for nearly 60 days.
Inputs
Results
A handheld Arduino device drawing 150mA from a 9000mAh power bank lasts about 54 hours — over 2 days of continuous use at 88% regulator efficiency.
Several real-world factors reduce battery life: (1) Peak current spikes — radios, motors, and displays briefly draw much more than average; (2) Temperature — battery capacity drops in cold environments; (3) Aging — rechargeable batteries lose 2–5% capacity per charge cycle; (4) Self-discharge — batteries slowly lose charge even when not connected; (5) Voltage cutoff — usable capacity ends before the battery is chemically exhausted. Apply a 20–30% derating factor for realistic estimates.
For ultra-low-power IoT projects requiring multi-year life: primary lithium cells (AA Energizer Ultimate Lithium) offer 3000mAh with extremely low self-discharge (~1%/year) and operate from −40°C to +60°C. For rechargeable projects: LiPo/Li-ion offer high energy density. For coin cell applications (simple sensors): CR2032 (225mAh) paired with ultra-low-power MCUs like nRF52 can last 5+ years at microamp average currents.
Use weighted average: I_avg = (I_active × t_active + I_sleep × t_sleep) / (t_active + t_sleep). Example: Arduino wakes every 8 seconds for 50ms (draws 15mA), sleeps remainder (draws 6µA). I_avg = (15 × 0.05 + 0.006 × 7.95) / 8 = (0.75 + 0.0477) / 8 ≈ 0.0997mA ≈ 100µA. A 1000mAh battery lasts 10,000 hours ≈ 1.1 years.
C-rate describes how fast a battery is discharged relative to its capacity. 1C means full discharge in 1 hour (2000mAh battery at 2000mA). 0.1C is a gentle discharge over 10 hours. Higher C-rates reduce available capacity due to internal resistance losses (Peukert effect). Li-ion batteries perform best below 0.5C. For very high current loads, derate the effective capacity — a battery discharged at 2C may only deliver 80% of its rated capacity.
Yes — batteries of the same type, chemistry, and state of charge can be connected in parallel to add their capacities. Two 2000mAh 3.7V LiPo cells in parallel give 4000mAh at 3.7V. Voltage stays the same; capacity doubles. However, always use cells from the same batch and charge level to prevent unbalanced charging. For Li-ion/LiPo, use a BMS (Battery Management System) for safe parallel operation.
The most common method for hobby projects: (1) Break the battery circuit and insert a multimeter set to mA range in series. (2) Use a USB power meter (like the UM25C) for USB-powered projects — measures voltage, current, and power in real time. (3) Use a dedicated power profiler like the Nordic PPK2 or Otii Arc for precise measurement of microamp sleep currents and millisecond-scale current spikes. (4) Measure voltage across a known small resistor (e.g., 1Ω) using an oscilloscope.
Critical LiPo safety rules: (1) Never discharge below 3.0V per cell — use a low-voltage cutoff circuit or battery protection board. (2) Never overcharge above 4.2V per cell — use a proper CC/CV charger (TP4056 IC is popular for hobby use). (3) Never puncture, crush, or short-circuit. (4) Do not charge unattended or in flammable environments. (5) Use batteries with built-in protection circuits (PCB) for simple projects. LiPo fires are rare but severe — take precautions seriously.
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