Battery Runtime Estimator
Reference Tables
Common Battery Capacities
Typical Device Loads
How It Works
Battery runtime is calculated by dividing the usable capacity by the current drawn by the device:
Runtime (hours) = (Capacity × Safety Factor) ÷ Load Current
- Capacity is measured in mAh or Ah. We normalize to Ah internally.
- Safety Factor prevents full discharge. 85% means only 85% of capacity is used.
- Power mode converts watts to current: Current = Power / Voltage.
Why real-world runtime differs
Temperature, battery age, discharge rate (Peukert's law), and conversion losses all affect actual runtime. High current draw reduces effective capacity compared to slow discharge. These estimates assume constant load under ideal conditions.
Frequently Asked Questions
What safety factor should I use?
For Li-ion and LiFePO4 batteries, 80-90% is generally safe. For lead-acid batteries, 50% is recommended for maximum lifespan. Set 100% only for theoretical maximum runtime.
Why is my real-world runtime shorter than calculated?
Temperature, battery age, discharge rates (Peukert's law), self-discharge, and conversion losses all affect capacity. High current draw typically reduces effective capacity compared to slow discharge.
How do I find my device's current draw?
Check the device datasheet, label, or power adapter rating. For USB devices, you can use a USB power meter. For battery-powered electronics, measure with a multimeter in series.
Is this calculator accurate for lithium batteries?
This provides a good estimate for constant-load scenarios. Lithium batteries maintain relatively stable voltage throughout discharge, making the linear calculation reasonably accurate. For variable loads, actual runtime will differ.
Privacy & Limitations
- All calculations run entirely in your browser -- nothing is sent to any server.
- Results are computed using standard formulas and should be verified for critical applications.
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Battery Runtime Calculator FAQ
What is Battery Runtime Calculator?
Battery Runtime Calculator is a free engineering & physics tool that helps you Estimate battery life based on capacity, load, and safety factor.
How do I use Battery Runtime Calculator?
Enter your input values, review the calculated output, and adjust inputs until you reach the result you need. The result updates in your browser.
Is Battery Runtime Calculator private?
Yes. Calculations run locally in your browser. Inputs are not uploaded to a server by default, and refreshing the page clears session data.
Does Battery Runtime Calculator require an account or installation?
No. You can use this tool directly in your browser without sign-up or software installation.
How accurate are results from Battery Runtime Calculator?
This tool applies standard formulas or deterministic processing logic for estimates. For medical, legal, tax, or investment decisions, verify with a qualified professional.
Can I save or share outputs from Battery Runtime Calculator?
You can bookmark this page and copy outputs manually. Results are not persisted in your account and are typically not embedded in the URL.