Lithium-Ion Battery Calculator

The Lithium-Ion Battery Calculator works out the full electrical profile of a custom battery pack based on how individual cells are wired together. Enter your cell capacity, nominal cell voltage, max/min cell voltages, battery chemistry, cells in series (S), and groups in parallel (P) to get the total pack capacity in Ah. Secondary outputs include pack voltage, max and min pack voltage, total energy (Wh), total cell count, C-rate at load, and the standard pack notation (e.g. 3S2P).

mAh

Individual cell capacity in milliamp-hours

V

Nominal voltage per cell

V

Fully charged cell voltage

V

Cutoff voltage per cell

S

Number of cells connected in series for higher voltage

P

Number of parallel groups for higher capacity

A

Expected load current draw

Results

Total Pack Capacity

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Pack Voltage (Nominal)

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Max Pack Voltage

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Min Pack Voltage

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Total Energy

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Total Cells

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C-Rate at Load

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Pack Notation

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Frequently Asked Questions

How do I calculate the total capacity of a lithium-ion battery pack?

Total pack capacity equals the individual cell capacity multiplied by the number of parallel groups. For example, if you have 3500mAh cells with 2 parallel groups, your pack capacity is 7000mAh or 7Ah.

What's the difference between series and parallel connections in battery packs?

Series connections (S) increase voltage by adding cell voltages together, while parallel connections (P) increase capacity by adding cell capacities together. A 3S2P pack has 3 cells in series and 2 parallel groups.

How do I determine the right voltage for my lithium-ion battery pack?

Pack voltage is determined by multiplying the nominal cell voltage by the number of series cells. Common configurations include 1S (3.7V), 2S (7.4V), 3S (11.1V), and 4S (14.8V) for different applications.

What is C-rate and why is it important for battery design?

C-rate represents the discharge rate relative to battery capacity. A 1C rate means the battery discharges its full capacity in 1 hour. Higher C-rates require cells rated for high discharge currents to avoid overheating and damage.

What's the difference between Li-ion and LiFePO4 batteries?

Li-ion batteries typically have higher energy density (3.7V nominal) but LiFePO4 batteries are safer and have longer cycle life (3.2V nominal). LiFePO4 also has a flatter discharge curve and better thermal stability.

How do I calculate the energy capacity in watt-hours (Wh)?

Energy in watt-hours equals capacity (Ah) multiplied by voltage (V). For example, a 7Ah, 11.1V battery pack contains 77.7Wh of energy, which determines runtime for your application.

What safety considerations should I have for lithium-ion battery packs?

Always use a Battery Management System (BMS) to protect against overcharge, over-discharge, overcurrent, and cell imbalance. Proper fusing, temperature monitoring, and quality cell selection are essential for safe operation.

How do I read battery pack notation like 18650 3S2P?

The notation describes the configuration: 18650 refers to the cell size, 3S means 3 cells in series, 2P means 2 parallel groups. This creates a pack with 6 total cells arranged in a 3S2P configuration.