18650 Battery Series and Parallel: Understanding S and P Configurations

[erikwong]

When several 18650 cells are combined into one battery pack, the cells can be connected in series, parallel, or a combination of both.

This is where terms such as 10S2P, 10S4P, and 13S4P come from.

The basic idea is simple. Series connections increase voltage, while parallel connections increase capacity and help distribute the load across more cells. A battery pack can then combine both methods to reach the voltage, capacity, and current required by the application.

For anyone designing or sourcing a custom 18650 battery pack, understanding S and P configurations is one of the most useful starting points.

What Do S and P Mean on 18650 Battery Pack?​

The letters are straightforward:

• S = Series
• P = Parallel

The number before S tells you how many cells or parallel groups are connected in series.

The number before P tells you how many cells are connected in parallel within each group.

For example:

10S2P

means 10 series groups, with 2 cells in parallel in each group.

The total number of cells is:

10 × 2 = 20 cells

A 13S4P pack contains:

13 × 4 = 52 cells

The S/P notation therefore gives engineers a quick way to describe the basic structure of a battery pack.

What Happens When 18650 Cells Are Connected in Series?​

A series connection adds the voltage of the cells.

Suppose one 18650 cell has a nominal voltage of 3.6V.

Two cells in series provide approximately:

3.6V × 2 = 7.2V

Ten cells in series provide:

3.6V × 10 = 36V

Thirteen cells provide:

3.6V × 13 = 46.8V

The same principle applies to the maximum charging voltage.

If the cell’s specified maximum charging voltage is 4.2V, a 10S configuration reaches:

4.2V × 10 = 42V

A 13S configuration reaches:

4.2V × 13 = 54.6V

This is why the series count must match the charger, BMS, and equipment.

For a more detailed explanation of nominal and full-charge voltage, see [18650 Battery Voltage: 3.6V vs 3.7V and 4.2V Explained].

What Happens When 18650 Cells Are Connected in Parallel?​

Parallel connections work mainly with capacity and current sharing.

Suppose one cell has a capacity of 3000mAh.

Two cells in parallel provide approximately:

3000mAh × 2 = 6000mAh

Four cells provide:

3000mAh × 4 = 12000mAh

The voltage remains approximately the same as one cell.

So a 1P group made from a 3.6V 3000mAh cell is approximately:

3.6V / 3Ah

A 4P group is approximately:

3.6V / 12Ah

The voltage has not become 14.4V. The capacity has increased instead.

This difference between series and parallel is the key concept behind most multi-cell battery packs.

Series vs Parallel at a Glance​

Connection	Main Effect	Voltage	Capacity
1S1P	Single cell	Cell voltage	Cell capacity
Series	Increases voltage	Higher	Essentially unchanged
Parallel	Increases capacity	Essentially unchanged	Higher
Series + Parallel	Adjusts both	Higher	Higher

This simple table explains why most practical 18650 packs use both S and P.

A battery for a low-voltage device may require only a few cells, while an e-bike or industrial battery may use dozens of cells in a larger S/P arrangement.

How Does 10S4P Battery Pack Work?​

10S4P is a useful example because it shows both connections at the same time.

Imagine four 18650 cells connected in parallel.

That creates one 4P group.

Now create ten identical groups and connect those groups in series.

The result is:

10S4P

Using 3.6V, 3000mAh cells:

• Nominal voltage: 36V
• Capacity: 12Ah
• Total cells: 40

The physical cell count is:

10 × 4 = 40 cells

The 10 series groups determine the voltage.

The four cells in each group determine the capacity and help share the load.

How Does a 13S4P Battery Pack Work?​

A 13S4P battery uses the same basic idea but has more series groups.

Using 3.6V, 3000mAh cells:

13 × 3.6V = 46.8V nominal

And:

4 × 3Ah = 12Ah

The total cell count is:

13 × 4 = 52 cells

So the simplified configuration is:

13S4P / 46.8V / 12Ah / 52 cells

This is a common type of configuration for a 48V-class lithium-ion battery.

The commercial label may say “48V,” while the detailed engineering specification uses the actual nominal voltage and maximum charging voltage.

Why Not Simply Connect More Cells in Series?​

Adding more cells in series increases voltage.

That sounds useful, but it also changes the requirements for the entire battery system.

A higher series count can require:

• A different BMS
• A different charger
• More cell voltage monitoring
• Different insulation requirements
• Different equipment voltage compatibility
• More attention to cell balancing

The series count should therefore be selected from the requirements of the equipment rather than simply adding cells to obtain a higher voltage.

Why Add More Cells in Parallel?​

There are two common reasons.

The first is higher capacity.

If one cell provides 3Ah, four cells in parallel provide approximately 12Ah.

The second is load sharing.

A larger parallel group can distribute current across more cells. This can be important for applications with higher continuous or peak current demands.

However, the actual current capability of the pack depends on the cell’s specifications, temperature, BMS, connections, thermal design, and other factors.

The P count should not be selected from a simple current multiplication alone.

For more information, see [18650 Battery Discharge Current: What Buyers Should Check].

How S/P Configuration Affects Battery Capacity​

The basic capacity relationship is:

Pack Capacity ≈ Cell Capacity × P

The series count does not directly multiply the Ah rating.

For example, using 3000mAh cells:

10S1P = 3Ah

10S2P = 6Ah

10S3P = 9Ah

10S4P = 12Ah

The voltage changes with the S count, while the capacity changes with the P count.

This is why a 10S4P pack and a 13S4P pack can both have 12Ah when they use the same 3000mAh cells, even though their voltage is different.

How S/P Configuration Affects Energy​

Battery energy is approximately:

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

For a 10S4P pack using 3000mAh cells:

36V × 12Ah = 432Wh

For a 13S4P pack:

46.8V × 12Ah = 561.6Wh

Both packs have the same nominal capacity of 12Ah.

The 13S4P pack contains more energy because its nominal voltage is higher.

This is an important distinction when comparing battery specifications. Looking only at Ah can give an incomplete picture.

For a detailed explanation, see [How Much Energy Does an 18650 Battery Hold? A Simple Wh Guide].

Common 18650 S/P Configurations​

Here are some simplified examples using 3.6V, 3000mAh cells:

Configuration	Nominal Voltage	Capacity	Total Cells
5S2P	18V	6Ah	10
7S2P	25.2V	6Ah	14
10S2P	36V	6Ah	20
10S4P	36V	12Ah	40
13S2P	46.8V	6Ah	26
13S4P	46.8V	12Ah	52
13S6P	46.8V	18Ah	78
14S4P	50.4V	12Ah	56

These numbers are simplified examples.

The actual battery design needs to consider the selected cell, operating current, charger, BMS and mechanical layout.

10S2P vs 10S4P: What Is the Difference?​

Both configurations have the same series count.

Therefore, assuming the same cells, they have approximately the same nominal voltage.

The difference is the parallel count.

10S2P​

Using 3000mAh cells:

• 36V nominal
• 6Ah
• 20 cells

10S4P​

Using the same cells:

• 36V nominal
• 12Ah
• 40 cells

The 10S4P battery has twice the capacity and twice the number of cells.

It will also normally be larger and heavier.

This is a simple example of how the P count changes the physical size of a battery.

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