Battery Runtime Estimator

Battery Runtime Calculator

Estimate how long your battery will last under load. Calculate by current draw or device power consumption, and account for system efficiency.

85%
Estimated Battery Runtime

0 Days, 21 Hours, 15 Mins

(Usable capacity accounts for efficiency losses)
Usable Battery Capacity: 2125 mAh
Equivalent Current Draw: 100 mA
Total Wh Energy: 9.25 Wh
Discharge C-rate: 0.04 C
Hours / Minutes formats: 21.25 hr / 1275 min
21.2h BATTERY DEVICE LOAD 100 mA

How to Use

1

Select Calculation Mode

Choose between By Current Draw (if you know milliamperes) and By Power Consumption (if you know Watts and Voltage).

2

Enter Battery & Load

Fill in your Battery Capacity (presets like 18650, AA are available) and define the operating load drawing power.

3

Adjust Efficiency

Use the efficiency slider to factor in real-world losses (heat, wiring, regulator drop). Default is a realistic 85%.

Battery Runtime Explanation

Runtime Formula: Runtime (hours) = (Capacity × Efficiency) / Load

Under ideal conditions, a battery with a capacity of 1000 mAh should last 10 hours if driving a load of 100 mA. However, real-world battery runtime is reduced by conversion inefficiencies in voltage regulators, wiring resistance, heat loss, temperature changes, and chemical aging. Setting efficiency to 80-85% is a standard baseline for typical DIY and electronic engineering designs.

Key Electrical Concepts:
  • Discharge rate (C-rate): Defines how fast a battery is being discharged. A rate of 1C means the discharge current will empty the battery in exactly 1 hour. A rate of 2C means it will empty in 30 minutes, whereas 0.5C corresponds to 2 hours.
  • Usable Capacity & DoD: Different batteries have safe Depth of Discharge (DoD) thresholds. For example, discharging Lead-Acid cells past 50% capacity severely limits their lifespan, whereas Lithium chemistries can easily support 80% to 90% DoD.
  • Peukert's Law: Alkaline and Lead-Acid battery capacities decrease as the discharge rate increases. If you discharge a battery very fast, its effective capacity shrinks.

Typical Battery Reference Capacities

Battery Type / Size Typical Voltage Standard Capacity Range Common Applications
CR2032 Coin Cell 3.0 V 200 – 240 mAh Watches, RTC Clocks, Key Fobs
AAA Alkaline 1.5 V 800 – 1200 mAh Remotes, Small Toys, Flashlights
AA Alkaline 1.5 V 1800 – 2600 mAh Wall Clocks, Cameras, Handheld Devices
9V Alkaline (6LR61) 9.0 V 500 – 600 mAh Smoke Detectors, Multimeters, Guitar Pedals
18650 Li-Ion 3.7 V 2200 – 3500 mAh Power Banks, Laptops, Flashlights, EV Cells
Lead Acid (12V 7Ah) 12.0 V 7 Ah (7000 mAh) UPS systems, Backups, Solar Inverters

Battery Runtime Formula Table

Calculation Mode Formula
Current Draw Mode Runtime (h) = (Capacity (Ah) × (Efficiency % / 100)) / Current (A)
Power Consumption Mode Runtime (h) = (Capacity (Ah) × Voltage (V) × (Efficiency % / 100)) / Power (W)
Discharge C-Rate C-rate = Current Draw (A) / Capacity (Ah)

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