18650 Battery Pack Calculator

Battery Pack Equations:

\[ \text{Pack Capacity (Ah)} = \text{Cell Ah} \times \text{Parallel Cells} \] \[ \text{Pack Voltage (V)} = \text{Cell Voltage} \times \text{Series Cells} \]

Cell Capacity (Ah):

Parallel Cells:

cells

Cell Voltage (V):

Series Cells:

cells

Pack Capacity:

Pack Voltage:

Pack Energy:

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1. What is an 18650 Battery Pack?

An 18650 battery pack is a collection of individual 18650 lithium-ion cells (18mm diameter, 65mm length) connected in series and/or parallel to achieve desired voltage and capacity. These packs are commonly used in electric vehicles, power tools, and energy storage systems.

2. How Does the Calculator Work?

The calculator uses these fundamental equations:

\[ \text{Pack Capacity (Ah)} = \text{Cell Ah} \times \text{Parallel Cells} \] \[ \text{Pack Voltage (V)} = \text{Cell Voltage} \times \text{Series Cells} \] \[ \text{Pack Energy (Wh)} = \text{Pack Capacity} \times \text{Pack Voltage} \]

Where:

Cell Ah — Capacity of a single cell in amp-hours
Parallel Cells — Number of cells connected in parallel
Cell Voltage — Nominal voltage of a single cell (typically 3.6-3.7V for Li-ion)
Series Cells — Number of cells connected in series

Explanation: Parallel connections increase capacity while keeping voltage the same. Series connections increase voltage while keeping capacity the same.

3. Importance of Pack Calculations

Details: Proper pack calculations are essential for designing battery systems that meet voltage requirements, capacity needs, and safety standards. They help determine runtime, power output, and charging parameters.

4. Using the Calculator

Tips: Enter the specifications of your individual 18650 cell, then specify how many cells will be connected in parallel and in series. Typical 18650 cells range from 2.0Ah to 3.5Ah capacity with 3.6V-3.7V nominal voltage.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between series and parallel connections?
A: Series increases voltage (V × number of cells), parallel increases capacity (Ah × number of cells).

Q2: What is a typical 18650 cell capacity?
A: Common capacities range from 2000mAh (2.0Ah) to 3500mAh (3.5Ah), with high-performance cells up to 4.0Ah.

Q3: What voltage should I use for calculations?
A: Use nominal voltage (typically 3.6V or 3.7V for Li-ion), not fully charged voltage (4.2V).

Q4: How do I calculate pack runtime?
A: Runtime (hours) ≈ Pack Capacity (Ah) ÷ Load Current (A). A 10Ah pack powering a 2A load would last ~5 hours.

Q5: What about battery management systems (BMS)?
A: All lithium-ion packs should include a BMS for safety. This calculator doesn't account for BMS power consumption.