Peukert's Law Calculator

Enter your battery's Rated Capacity (Ah), Rated Discharge Rate (A), Peukert Number, and Actual Discharge Rate (A) into the Peukert's Law Calculator to find your real-world Discharge Time, along with Effective Capacity, Capacity Reduction, and Discharge Efficiency — because your battery almost never delivers what the label promises.

Ah

Battery capacity at standard rating conditions

A

Discharge current at which capacity is rated

Typically 1.1-1.3 for lead-acid, 1.05-1.15 for lithium

A

Current draw for your application

Results

Discharge Time

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Effective Capacity

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Capacity Reduction

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Discharge Efficiency

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Battery Capacity Distribution

Frequently Asked Questions

What is Peukert's Law and why is it important?

Peukert's Law describes how a battery's effective capacity decreases as the discharge rate increases. It's crucial for accurately predicting battery runtime in real-world applications where discharge rates vary from the rated conditions.

What is the typical Peukert number for different battery types?

Lead-acid batteries typically have Peukert numbers between 1.1-1.3, with higher values for older or lower-quality batteries. Lithium batteries perform better with Peukert numbers around 1.05-1.15, while AGM batteries fall in between at 1.15-1.25.

How does discharge rate affect battery capacity?

Higher discharge rates reduce effective battery capacity due to internal resistance and chemical reaction limitations. A battery rated at 100Ah at 5A discharge might only deliver 80Ah when discharged at 20A, depending on its Peukert number.

Can I use this calculator for any battery chemistry?

Yes, but you need the correct Peukert number for your specific battery type and model. The manufacturer's datasheet or battery testing can provide this value, as it varies significantly between different chemistries and designs.

Why is my actual battery runtime shorter than calculated?

Real-world factors like temperature, battery age, depth of discharge limits, and inverter efficiency can further reduce runtime. Peukert's Law accounts for discharge rate effects but doesn't include these additional factors.

How do I find my battery's Peukert number if it's not specified?

You can estimate it by testing discharge times at different current levels, or use typical values: 1.3 for flooded lead-acid, 1.2 for AGM, 1.15 for gel, and 1.1 for lithium. Conservative estimates help ensure adequate battery sizing.

Does temperature affect Peukert calculations?

Temperature significantly affects battery performance, but Peukert's Law primarily addresses discharge rate effects. Cold temperatures increase the effective Peukert number, while warm temperatures decrease it, requiring separate temperature correction factors.

Should I size my battery bank based on Peukert-adjusted capacity?

Absolutely. Using the manufacturer's rated capacity without Peukert correction often leads to undersized battery banks. Always calculate effective capacity at your actual discharge rates for proper system design and reliable operation.

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