Battery Pack Capacity Calculator

Calculator Inputs

Battery Chemistry

Custom Cell Nominal Voltage (V)

Custom Cell Max Voltage (V)

Custom Cell Min Voltage (V)

Cell Capacity (mAh)

Cells in Series (S)

Parallel Strings (P)

Depth of Discharge (%)

Pack Efficiency (%)

Reserve Buffer (%)

Temperature Derating (%)

Load Power (W)

Load Current (A, optional)

Cell Weight (g, optional)

Cost per Cell ($, optional)

Plotly Runtime Graph

This graph estimates runtime across a range of power loads using your calculated usable energy.

Example Data Table

Chemistry	Cell Capacity	Configuration	Pack Voltage	Pack Capacity	Nominal Energy	Usable Energy	Load Power	Runtime
Lithium-ion (NMC/NCA)	3000 mAh	4S2P	14.80 V	6.00 Ah	88.80 Wh	72.14 Wh	120 W	0.60 h
LiFePO4	2800 mAh	8S1P	25.60 V	2.80 Ah	71.68 Wh	58.03 Wh	80 W	0.73 h
NiMH	2500 mAh	10S3P	12.00 V	7.50 Ah	90.00 Wh	69.26 Wh	60 W	1.15 h

Formula Used

Pack Capacity (Ah)
Cell Capacity (Ah) × Parallel Strings

Pack Capacity (mAh)
Cell Capacity (mAh) × Parallel Strings

Pack Nominal Voltage (V)
Cell Nominal Voltage × Series Cells

Pack Max Voltage (V)
Cell Max Voltage × Series Cells

Nominal Energy (Wh)
Pack Nominal Voltage × Pack Capacity (Ah)

Usable Factor
DoD × Efficiency × Temperature Derating × (1 − Reserve)

Usable Energy (Wh)
Nominal Energy × Usable Factor

Runtime (h)
Usable Energy ÷ Load Power

The calculator assumes balanced cells and a stable average load. Real systems can differ due to aging, discharge rate limits, internal resistance, wiring losses, and battery management rules.

How to Use This Calculator

Select a battery chemistry or choose custom values.
Enter single-cell capacity in mAh.
Enter series cells to set pack voltage.
Enter parallel strings to set pack capacity.
Add discharge, efficiency, reserve, and temperature assumptions.
Enter load power for runtime estimation.
Optionally enter current, weight, and cost.
Press calculate to view results, graph, and export options.

Frequently Asked Questions

1. What does series configuration change?

Series cells increase pack voltage. Capacity in amp-hours stays the same for each parallel path. Higher series count raises nominal, maximum, and minimum pack voltage.

2. What does parallel configuration change?

Parallel strings increase total capacity and current capability. Pack voltage stays the same, but amp-hours, milliamp-hours, and energy increase in direct proportion.

3. Why is usable energy lower than nominal energy?

Usable energy accounts for discharge limits, efficiency losses, reserve buffer, and temperature derating. These factors make practical output lower than theoretical stored energy.

4. Should I enter both load power and load current?

You can enter power alone for a quick estimate. Enter current too when your device specification is current-based or when you want a separate current runtime result.

5. Is this suitable for lithium, NiMH, and lead-acid cells?

Yes. Presets cover several common chemistries, and custom mode supports others. Always verify manufacturer discharge limits and voltage windows before final design.

6. Why include a reserve buffer?

Reserve helps prevent full depletion, supports longevity, and leaves emergency energy available. Designers often keep some capacity unused for reliability and pack protection.

7. Does temperature really affect capacity?

Yes. Cold or extreme conditions can reduce available energy and increase resistance. The derating field lets you model those real-world losses conservatively.

8. Can I use this for final engineering approval?

Use it for sizing, comparison, and planning. Final approval should also consider thermal limits, BMS rules, safety standards, cell matching, and cycle-life testing.