Series-Parallel Combinations: How to Calculate Total Voltage and Capacity for 3S2P, 4S3P Packs

If you’ve ever shopped for a lithium-ion battery pack and felt confused by labels like “3S2P 11.1V 5200mAh” or “4S3P 14.8V 9000mAh,” you’re not alone. The “S” and “P” notation is the universal shorthand for how cells are wired inside a pack, but without understanding the calculation logic behind it, those numbers can feel like a foreign language.

Once you understand series-parallel calculation, you gain control over your own pack designs — whether you’re building a DIY power bank, upgrading an e-bike battery, assembling a solar storage system, or engineering a custom industrial power solution. You’ll know exactly what voltage and capacity to expect before you ever touch a spot welder.

Let’s break down the calculation method, work through real-world examples including 3S2P and 4S3P configurations, cover the LiFePO₄ voltage variant, and address the most common mistakes that trip up both beginners and experienced builders.

What “S” and “P” Actually Mean

The notation is straightforward once you know the code:

• S = Series. Cells connected positive-to-negative in a chain. Series adds voltage.

• P = Parallel. Cells connected positive-to-positive and negative-to-negative. Parallel adds capacity and current capability.

• S × P = Total cell count. A 3S2P pack contains 3 × 2 = 6 cells. A 4S3P pack contains 4 × 3 = 12 cells.

The notation typically reads as “how many in series × how many parallel strings.” So 3S2P means: three cells connected in series to form one string, and two such strings connected in parallel. Some manufacturers use the reverse convention (2P3S), but the math works identically — voltage is always determined by the series count, and capacity is always determined by the parallel count.

Battery packs are assembled in series and parallel to achieve the voltage and capacity a particular application requires. If higher voltage is needed, cells are added in series. If higher current capacity or longer runtime is needed, cells are added in parallel.

The Two Rules That Govern Everything

There are exactly two rules you need to memorize:

Rule 1: Series adds voltage.
Total Pack Voltage = Single Cell Nominal Voltage × Number of Series Cells (S)

Rule 2: Parallel adds capacity (and current).
Total Pack Capacity = Single Cell Capacity × Number of Parallel Strings (P)

These rules are universal across all lithium-ion chemistries — NMC, NCA, LiFePO₄, and LCO alike. What changes between chemistries is the single-cell voltage you plug into the formula for total pack power.

The voltage of a series string equals the cell voltage multiplied by the number of cells in that string, while the capacity stays the same as a single cell. For parallel groups, the voltage equals a single cell’s voltage, but the capacity equals the cell capacity multiplied by the number of parallel cells.

Standard Calculation: 3S2P with 3.7V NMC Cells (the most common configuration)

Let’s work through the most common lithium-ion battery pack configuration on the market — 3S2P with standard NMC 18650 or 21700 cells.

The setup:

• Cell nominal voltage: 3.7V

• Cell capacity: 2600mAh per cell

• Configuration: 3S2P (3 series × 2 parallel)

Step 1: Calculate pack voltage.
Total voltage = Cell voltage × Number of series cells
Total voltage = 3.7V × 3 = 11.1V nominal

Step 2: Calculate pack capacity.
Total capacity = Cell capacity × Number of parallel strings
Total capacity = 2600mAh × 2 = 5200mAh

Step 3: Verify total cell count.
3S × 2P = 6 cells total

Final pack specs: 11.1V, 5200mAh, 6 cells

This is why you commonly see commercial 3S2P packs rated at 11.1V and 5200mAh. The math always traces back to the individual cell specs arranged in the 3S2P structure.

The 3.6V variant: Some manufacturers use 3.6V instead of 3.7V as the nominal cell voltage. The calculation is identical — just swap the base number:

• 3.6V × 3 = 10.8V

This is why you’ll occasionally see 3S packs labeled both 10.8V and 11.1V. Both are correct — they simply reflect different choices for the nominal cell voltage in the calculation. We’ve explored this 3.6V vs 3.7V distinction in detail in our previous guide on 18650 battery voltage: the truth about 3.6V vs 3.7V.

Regardless of whether you use 3.6V or 3.7V for nominal calculations, the full charge voltage is what matters for charger and BMS selection: 4.2V × 3 = 12.6V for any 3S NMC pack.

Higher Configurations: 3S3P, 4S2P, and 4S3P

Once you understand the rules, scaling up to larger packs is straightforward.

3S3P

The setup:

• Cell: 3.7V nominal, 3000mAh

• Configuration: 3S3P

Calculation:

• Voltage: 3.7V × 3 = 11.1V

• Capacity: 3000mAh × 3 = 9000mAh

• Cell count: 3 × 3 = 9 cells

4S2P

The setup:

• Cell: 3.7V nominal, 2200mAh

• Configuration: 4S2P

Calculation:

• Voltage: 3.7V × 4 = 14.8V (full charge: 4.2V × 4 = 16.8V)

• Capacity: 2200mAh × 2 = 4400mAh

• Cell count: 4 × 2 = 8 cells

This configuration is commonly found in laptop battery packs and cordless power tools. A group of 8 cells in 4S2P delivering 14.8V and 4400mAh is a classic example of this configuration.

4S3P

The setup:

• Cell: 3.7V nominal, 3000mAh

• Configuration: 4S3P

Calculation:

• Voltage: 3.7V × 4 = 14.8V (full charge: 16.8V)

• Capacity: 3000mAh × 3 = 9000mAh

• Cell count: 4 × 3 = 12 cells

Quick Reference: Common Configurations for NMC Cells (3.7V nominal)

Where “C” = single cell capacity in mAh or Ah. This table uses 3.7V nominal NMC cells as the base unit.

The LiFePO₄ Variant: Same Rules, Different Base Voltage

This is the single most common calculation mistake in DIY pack building. If you’re working with LiFePO₄ cells (also labeled IFR), the base voltage changes from 3.7V to 3.2V, and the full charge voltage changes from 4.2V to 3.65V.

Let’s recalculate the same configurations with LiFePO₄ cells:

LiFePO₄ 3S2P

• Voltage: 3.2V × 3 = 9.6V (full charge: 3.65V × 3 = 10.95V)

• Capacity: cell capacity × 2

A commercial 3S2P LiFePO₄ pack built with 32700 cells delivers 9.6V nominal and typically 12Ah capacity.

LiFePO₄ 4S1P

• Voltage: 3.2V × 4 = 12.8V (full charge: 3.65V × 4 = 14.6V)

• Capacity: cell capacity × 1

This is the standard configuration for “12V replacement” LiFePO₄ batteries. The 12.8V nominal closely matches the 12V lead-acid systems it’s designed to replace, while still delivering stable LiFePO₄ chemistry with 2,000–6,000+ cycle life.

LiFePO₄ 4S2P

• Voltage: 3.2V × 4 = 12.8V

• Capacity: cell capacity × 2

For anyone building or buying LiFePO₄ packs — whether for solar street lights, RV energy storage, marine house banks, or portable power stations — matching the voltage platform to the intended application is critical. Explore our IFR32140 LiFePO₄ battery collection for large-format cells with capacities from 10Ah to 20Ah, or browse our IFR32700 LiFePO₄ batteries for the 32700 form factor designed for high-power applications. Both collections feature genuine Grade-A cells from EVE and Lishen, with matched options available for multi-cell pack assembly.

⚠️ Critical safety note: Never mix LiFePO₄ and NMC cells in the same pack. The different voltage platforms (3.2V vs 3.7V nominal) create dangerous imbalances, and LiFePO₄’s 3.65V full charge is far below NMC’s 4.2V — using the wrong charger will permanently damage LiFePO₄ cells. For a deep dive into why LiFePO₄’s chemistry makes it the safest lithium option on the market, read our detailed guide on the olivine structure of LiFePO₄ and why it won’t explode or catch fire.

Calculating Watt-Hours (Wh): The Metric That Actually Compares Different Packs

Voltage and capacity are useful individually, but watt-hours (Wh) tell you the total energy stored regardless of configuration. This is the fairest way to compare packs with different voltages.

Formula: Total Wh = Pack Voltage × Pack Capacity (in Ah)

Let’s compare two common configurations built from the same cells (3.7V, 2500mAh):

3S2P:

• Voltage: 3.7V × 3 = 11.1V

• Capacity: 2500mAh × 2 = 5000mAh = 5Ah

• Energy: 11.1V × 5Ah = 55.5Wh

4S3P:

• Voltage: 3.7V × 4 = 14.8V

• Capacity: 2500mAh × 3 = 7500mAh = 7.5Ah

• Energy: 14.8V × 7.5Ah = 111Wh

The 4S3P pack stores exactly twice the energy of the 3S2P (111Wh vs 55.5Wh) — because it uses twice as many cells (12 vs 6). The Wh calculation simply confirms what the cell count already told you, but it becomes essential when comparing packs built from different cell types or capacities.

For maximum runtime in flashlights or energy storage systems, understanding the high-drain vs high-capacity cell trade-off is essential. Our high-drain vs high-capacity battery selection guide walks through exactly how internal resistance, mAh ratings, and continuous discharge current interact to determine real-world pack performance — not just what the label says.

Current Handling: How P Determines Maximum Discharge

Parallel connections don’t just add capacity — they multiply current capability. This is a crucial concept for high-drain applications.

Formula: Total Max Continuous Current = Single Cell CDR × Number of Parallel Strings (P)

Example: A 3S3P pack built with Molicel P28A cells (2800mAh, 35A true CDR) delivers:

• Max continuous current: 35A × 3 = 105A

• Voltage: 3.7V × 3 = 11.1V

• Total capacity: 2800mAh × 3 = 8400mAh

This is why high-performance e-skateboard packs, competition drone batteries, and cordless power tool packs are often built in 3P, 4P, or even 5P configurations — each additional parallel string multiplies the total current delivery capability while the voltage remains fixed by the series count.

Common Mistakes (and How to Avoid Them)

Mistake 1: Adding both voltage and capacity when cells are in parallel.
Two 3.7V 3000mAh cells in parallel give you 3.7V and 6000mAh — not 7.4V and 6000mAh. Voltage stays flat in parallel; only capacity multiplies. The same error happens in the other direction: three 3.7V cells in series give you 11.1V and whatever capacity a single cell has — not 11.1V and triple the capacity.

Mistake 2: Forgetting that capacity in series stays at the single-cell level.
A 3S1P pack built with 3000mAh cells is a 3000mAh pack, not a 9000mAh pack. The Ah rating doesn’t multiply through series connections — only parallel strings increase capacity.

Mistake 3: Using the wrong nominal voltage for LiFePO₄.
LiFePO₄ cells are 3.2V nominal, not 3.7V. If you calculate a 4S LiFePO₄ pack at “14.8V” instead of “12.8V,” you’ll select the wrong charger and potentially damage your cells. Always verify chemistry before calculating.

Mistake 4: Mixing unequal cells.
In series configurations, the total capacity is limited by the weakest cell in the string. If one cell hits its discharge cutoff before the others, the entire string must stop delivering power — even if the other cells still have usable capacity remaining. In parallel, mismatched cells create constant internal discharge from the higher-voltage cells into the lower-voltage ones, generating waste heat and accelerating degradation. Always use matched cells with identical capacity, internal resistance, and state of charge in any pack build. When building packs, use a quality charger that maintains cell balance — browse our battery chargers for options with independent channel charging and automatic chemistry detection.

Mistake 5: Assuming configuration order doesn’t matter.
Connecting cells first in series versus first in parallel does matter — it affects BMS complexity and pack behavior, particularly when cells aren’t perfectly matched. Generally, building parallel groups first (and then connecting those groups in series) requires fewer BMS balance leads, resulting in lower cost and simpler wiring.

Mistake 6: Confusing Ah with Wh when comparing packs.
A 3S2P 11.1V 6000mAh pack and a 4S2P 14.8V 6000mAh pack are not equivalent — the 4S2P pack stores 33% more energy (88.8Wh vs 66.6Wh) because the same capacity is delivered at a higher voltage. Always convert to watt-hours for apples-to-apples comparisons.

Real-World Verification: Spot the Math

Next time you encounter a commercial pack label, try reverse-engineering the cell specs. If you see a pack rated at “11.1V, 4400mAh, 3S2P,” you can work backwards:

• Single cell voltage: 11.1V ÷ 3 = 3.7V

• Single cell capacity: 4400mAh ÷ 2 = 2200mAh

• Total cells: 3 × 2 = 6

This works for any pack. A 12V 4400mAh 3S2P pack built with 18650 cells uses the configuration to deliver a 12V output compatible with most solar controllers, and a 3S2P structure gives the needed voltage (~12V) through 3 series cells while the 2 parallel strings stabilize capacity for overnight discharge cycles. Every commercial pack label — whether it’s for e‑bikes, scooters, solar lighting, or portable power — can be decoded using exactly this method.

Understanding these calculations is also the foundation of good pack design. Our guide on series vs parallel: foundational principles of battery pack design explains how the S and P arrangement affects everything from BMS complexity to failure behavior.

For all the cells, chargers, and accessories needed to build or upgrade your pack, visit our OneAndes complete store.

The Bottom Line

“S” multiplies voltage. “P” multiplies capacity and current capability. That’s the entire logic behind every battery pack label you’ll encounter. Whether you’re deciphering a commercial pack’s specs or designing your own, the formulas are simple:

• Pack Voltage = Cell Voltage × S

• Pack Capacity = Cell Capacity × P

• Pack Energy (Wh) = Pack Voltage × Pack Capacity (Ah)

• Max Current = Cell CDR × P

• Total Cells = S × P

Memorize these five equations, always verify whether your cells are 3.7V NMC or 3.2V LiFePO₄ before calculating, and only use matched cells in any configuration. Do those three things, and you’ll never misread a battery pack label or miscalculate a pack design again.