Battery Life Calculator
Calculate battery runtime from capacity (mAh) and device current draw. Estimate how long your battery will last in real-world conditions.
What is Battery Life Calculator?
This battery life calculator estimates how long a battery will power your device based on battery capacity (mAh/Wh) and average current draw (mA). Includes a Peukert effect correction for lead-acid batteries and accounts for real-world efficiency losses.
How to Use This Calculator
- Enter your Battery Capacity, Device Current Draw, Circuit Efficiency in the input fields provided
- Results are computed instantly as you enter or modify values — no need to click a button
- Review the computed output showing your battery life results with a detailed breakdown
- Use the output for preliminary design checks — critical applications require verification by a licensed professional
How Battery Life Calculator is Calculated
This calculator uses the formula: Hours = (Capacity_mAh × Efficiency%) / Current_draw_mA. Where LiPo nominal voltage = 3.7V ; Energy = Capacity × Voltage. Actual battery life is always less than theoretical due to efficiency losses and aging. All calculations run entirely in your browser — no data is transmitted to any server.
Frequently Asked Questions
How is battery life calculated?
Battery Life (hours) = Battery Capacity (mAh) / Device Current (mA) × 0.7 (efficiency factor). A 5,000 mAh phone battery drawing 400 mA average: 5000/400 × 0.7 = 8.75 hours of screen-on use.
Why does actual battery life differ from calculated?
Self-discharge (5–10%/month), temperature effects (cold reduces capacity 20–30%), aging (batteries lose 20% capacity after 500 cycles), and varying current draw (screen brightness, signal strength) all reduce actual runtime.
Related Calculators
Why Use This Calculator?
Engineering calculations require precision — errors can have real-world consequences. Battery Life Calculator uses validated formulas from engineering standards and textbooks. Whether you are designing systems, troubleshooting problems, or studying for engineering exams, this tool provides reliable results with clear methodology. All standard units are supported with automatic conversion.
What This Tool Offers
- Instant Battery Life Calculator calculation with validated formulas
- Detailed step-by-step result breakdown
- Works offline as a Progressive Web App
- Completely free — no signup or data collection
- Mobile-friendly responsive design
- Save and share your results easily
Expert Tips
- 💡 Always verify critical calculations with standard reference materials before implementation.
- 💡 Check units carefully — unit mismatches are the most common engineering error.
- 💡 For safety-critical applications, apply appropriate safety factors to calculated values.
- 💡 Understand the assumptions behind each formula — they have valid ranges of application.
- 💡 Use SI units for consistency and to avoid conversion errors.
Who Is This For?
Engineering students and professors, practicing engineers designing systems, technicians troubleshooting equipment, and hobbyists building projects.
📚 Complete Guide Available
Want to learn more? Read our comprehensive guide with detailed explanations, real-world examples, expert analysis, and actionable tips.
Read: BatterylifeEngineering disclaimer: This calculator provides preliminary estimates. All calculations for actual engineering projects must be verified by a licensed professional engineer. See our full Disclaimer.
Maintained by: Sagar Sahni, Calc Labz | Review: formula checks, worked examples, and periodic updates
Need a correction? Contact us with the calculator name, your inputs, and the issue you found.
Last updated: April 2026