Custom 18650 Battery Packs for OEM Equipment

Larnek Power builds custom 18650 battery packs for OEM manufacturers, product developers and industrial equipment makers. Every 18650 battery pack starts from your device: the voltage window it runs in, the runtime it needs, the current it draws and the space left for the battery. From there, our engineers choose the cell, the series-parallel configuration, the BMS and the connector – then build samples you can test in your own product.

This page covers what is specific to the 18650 cell format. For our full development scope across cell formats, see custom battery packs.

Since 2015

Custom battery pack projects

5,000 m²

Own factory

6 engineers

15+ years’ professional experience

60

Production-line employees

25+ countries

Traded with customers in

Is an 18650 Battery Pack the Right Choice for Your Device?

The 18650 is a cylindrical lithium-ion cell, 18 mm in diameter and 65 mm long, and one of the most widely produced cell formats. That gives pack designers a broad choice of cell models. Whether it is the right base for your 18650 lithium-ion battery pack depends on space, energy and current – not on habit.

Discuss Your Application

18650 usually fits when…

  • The housing is slim or narrow and the battery has to follow its shape.
  • You need fine steps in voltage or capacity – each 18650 cell is a small building block.
  • The load current can be shared across enough cells in parallel.
  • The product is compact or hand-held, so every millimetre and gram counts.

Look at 21700 when…

  • The pack needs more energy and the space allows a larger cell – fewer cells can mean fewer connections.
  • Sustained high current or long runtime dominates the design.

Compare both formats in 18650 vs 21700, or see custom 21700 battery packs.

Capacity-type or power-type 18650 cells?

Within the 18650 format, cells are optimised in different directions. Choosing the cell type early avoids a pack that meets its capacity on paper but sags under your real load.

18650 cell type
Optimised for
Trade-off
Typical fit

Capacity-type

Highest capacity per cell and runtime per volume

Lower continuous and pulse current rating

Instruments, monitoring units, low-to-moderate loads

Power-type (high-drain)

High continuous and pulse current with less voltage sag

Lower capacity per cell

Motors, pumps and other high-current loads

Balanced

A middle ground between capacity and current

Neither the longest runtime nor the highest current

General portable equipment

18650 Battery Pack Configurations: Voltage, Capacity and Layout

An 18650 battery pack configuration is written as xSyP: x cells in series set the voltage; y cells in parallel set the capacity and share the current. A 3S2P pack, for example, uses six cells – three series groups of two cells each.

How to calculate an 18650 pack’s voltage, capacity and energy

Nominal voltage: S × cell nominal voltage (typically 3.6–3.7 V)

Full-charge voltage: S × 4.2 V (standard Li-ion cells – check the datasheet)

Rated capacity: P × cell capacity (mAh or Ah)

Energy: Nominal voltage × capacity (Ah) = Wh

Cell count: S × P

Worked example: 4S1P with 3,000 mAh Cells

  • Voltage: 4 × 3.7 V = 14.8 V nominal (16.8 V full charge)
  • Capacity: 1 × 3.0 Ah = 3.0 Ah
  • Energy: 14.8 V × 3.0 Ah ≈ 44.4 Wh
  • Cells: 4 × 1 = 4 cells
  • Approx. pack size: 38 × 38 × 70 mm

Actual usable capacity and runtime depend on discharge current, temperature, BMS settings, cut-off voltage and the operating conditions of the device.

Common 18650 pack voltage classes

Series count
Nominal voltage*
Full-charge voltage
Often specified as
Cells in a 2P build

1S

3.6–3.7 V

4.2 V

3.7 V pack

2

2S

7.2–7.4 V

8.4 V

7.4 V pack

4

3S

10.8–11.1 V

12.6 V

11.1 V or “12 V” pack

6

4S

14.4–14.8 V

16.8 V

14.4 V / 14.8 V pack

8

6S

21.6–22.2 V

25.2 V

22.2 V pack

12

7S

25.2–25.9 V

29.4 V

“24 V” pack

14

* Reference values for 3.6–3.7 V nominal lithium-ion 18650 cells. “12 V” and “24 V” are labels: a 3S pack runs from 12.6 V when full down to its cut-off voltage, so we check that whole range against your device’s input window. Other series and parallel counts are reviewed per project for current, thermal and safety design.

Same cells, different pack

A 4S2P and a 2S4P pack both use eight cells and store the same energy. One delivers twice the voltage; the other twice the capacity and current capability. Your device’s voltage window decides which is correct – which is why we ask for the minimum and maximum input voltage, not just a nominal figure.

Fitting an 18650 Battery Pack Into Your Housing

Cell count fixes the electrical design; the layout decides whether the pack fits. With 18650 cells the same configuration can be arranged in several ways. In a straight row each extra cell adds about 18 mm side by side, or 65 mm end to end – before holders, insulation and the BMS.

18650 3S1P in-line stick battery pack, about 195 x 18 x 18 mm cells only

≈ 195 × 18 × 18 mm (cells only)

3S1P · in-line (stick) – long and narrow, for tube-shaped or handle compartments.

18650 3S1P flat battery pack 11.1V 2600mAh, 56 x 19 x 70 mm, with long BMS board

56 × 19 × 70 mm · 11.1 V 2600 mAh

3S1P · flat – the same three cells side by side as a short, flat pack, with a long BMS board along the top.

18650 4S1P flat battery pack 14.8V 2600mAh, 75 x 19 x 70 mm, with long BMS board

75 × 19 × 70 mm · 14.8 V 2600 mAh

4S1P · flat – one more cell in the row adds about 19 mm of width and one series step in voltage.

18650 3S1P triangle battery pack 11.1V 3000mAh, 37 x 37 x 66 mm, with long BMS board

37 × 37 × 66 mm · 11.1 V 3000 mAh

3S1P · triangle – three cells stacked in a triangle for a compact section in deeper housings.

What adds to the envelope beyond the cells

  • Cell holders or spacers between cells
  • Interconnect strips and weld tabs
  • The BMS board – its position at the end, side or top changes the outline
  • Insulation, edge protection and the outer wrap or housing
  • Wire exit, strain relief and connector position
  • Thermal clearance in high-current or warm installations

What helps us lay out your 18650 pack

  • Maximum length × width × height, plus any keep-out zones
  • Where the wires must exit and how the pack is held in place
  • Weight limit for the pack
  • A 2D drawing or 3D model (e.g. STEP) of the battery compartment

Pack structure and assembly are covered in more detail under battery pack design and assembly.

BMS, Connectors and Pack Format for 18650 Packs

The cells set what a pack can deliver; the BMS, harness and pack format decide how safely and simply it works inside your device.

  • 18650 4S2P battery pack 14.8V 6700mAh with customizable BMS and customized connector options
  • 18650 two-cell battery pack with BMS protection board and wiring harness
  • 18650 battery pack wiring harness with custom connector options

BMS & protection

An 18650 battery pack with BMS protection is matched to its series count and to your continuous and peak current. Protection typically covers over-charge, over-discharge, over-current, short circuit and temperature. Packs with several cells in series also need balancing to keep the series groups aligned over the pack’s life.

BMS integration

Connectors & wiring harness

We specify the connector, wire gauge, lead length and pin-out against your device’s mating connector and current, so the pack installs without adapters. Tell us whether charge and discharge share one port, and whether your device expects a temperature-sensor line or battery data from the pack.

Pack format

The format follows how your device carries the battery – from an insulated, wrapped cell block for an enclosed compartment to a pack in a protective housing where it is handled or exposed. Mounting method, vibration and operating temperature all feed into this choice.

Where Custom 18650 Battery Packs Are Used

The design priority changes with the equipment. These are the questions that usually shape an 18650 pack in each of our focus applications.

Custom 18650 battery pack applications: power tools, chainsaws, portable medical devices and golf carts
Custom 18650 battery pack applications: Bluetooth speakers, special-purpose equipment, industrial robots and electric skateboards
Custom 18650 battery pack applications: POS terminals, ventilators, electric wheelchairs and electric bicycles
Application
Main design driver
What we check in the 18650 design

Portable instruments

Size and weight

Layout options; capacity-type cells against the runtime target

Inspection & measurement devices

Stable supply through the whole run

Device minimum voltage against pack cut-off; series count

Communication equipment

Transmit pulses

Cell pulse-current rating, parallel count and voltage sag

Remote monitoring systems

Long intervals between service visits

Self-discharge, site temperature range and capacity margin

Emergency lighting

Standby duty

The luminaire’s charging method and the temperature inside the fitting

Cleaning equipment

Motor and pump load

Continuous current, cell type and thermal layout

Portable power equipment

Energy against carrying weight

Wh per kg trade-off and output current

Industrial equipment

Integration and repeat supply

Mounting, vibration and connector – see industrial battery packs

Equipment not listed? Describe it in your RFQ, or browse applications.

Larnek 18650 battery pack assembly workshop with technicians at welding and test stations
Prototype to Production

From 18650 Pack Sample to Volume Supply

Your 18650 pack follows the same route as every Larnek project: requirement analysis, cell selection, electrical and structural design, BMS integration, samples, testing and volume production. The step-by-step version is on our OEM & ODM battery pack development page. For 18650 packs, three points matter most:

Configuration agreed before samples

The proposed cell, xSyP configuration, layout and BMS are shared for your review before any sample is built.

Samples tested in your device

Prototype packs are checked for fit and function in your own product, then verified against the agreed specification.

Consistent repeat builds

The approved cell, configuration and BMS become the build specification for volume production.

Test reports and transport documents depend on the pack and the target market – pack energy in Wh is one of the inputs. We confirm which apply at quotation; see testing, certification and compliance.

Since 2015 · own factory of 5,000 m² · 6 engineers with 15+ years’ experience · 60 production-line employees · customers in 25+ countries. Learn more about Larnek Power as a custom battery pack manufacturer.

18650 Battery Pack FAQs

It is set by the number of cells in series. With standard 3.6–3.7 V lithium-ion 18650 cells, a 1S pack is 3.6–3.7 V nominal, a 3S pack about 11 V (usually called a 12 V pack) and a 7S pack about 25 V (usually called a 24 V pack). We choose the series count from your device’s minimum and maximum input voltage, not only the label.

Each cell added in parallel adds one cell’s capacity. The practical limit is your space, weight and current needs – and cells with higher capacity usually have lower current ratings. Tell us the runtime you need per charge and we will size the parallel count and cell type together.

Lithium-ion packs need protection against over-charge, over-discharge, over-current and short circuit, and multi-series packs also need balancing. In some products part of this protection already sits in the host device. We review where each function sits, so nothing is duplicated or missing. See BMS integration.

Send the cell model or your approved cell list with the RFQ. We review its fit for your current and temperature range and its availability for your volumes, then confirm it or propose alternatives with the trade-offs explained.

Mainly the cell count (S × P), the layout, and what surrounds the cells: holders, interconnects, the BMS board, insulation and any housing. A different arrangement of the same cells often solves a tight space, so send your compartment drawing and limits with your requirements.

No. Larnek Power develops custom 18650 battery packs for OEM and equipment projects, from samples to volume supply. We are not a retail battery shop. If you need a pack for equipment you build, send us your requirements.

Your Battery Pack, Built Safe, Compliant and On Time

Backed by a strong Shenzhen supply chain, a dedicated engineering team and hands-on export experience, Larnek Power helps OEM teams move custom battery packs into production with consistent quality, competitive cost and the paperwork export requires.

Request a Quote

Tell Us About Your Battery Project

Larnek Power supports OEM and industrial customers with custom 18650 and 21700 lithium-ion battery packs, from initial requirements and prototyping through volume production.

Tell us about your application, target voltage and capacity, size limits, current requirements, estimated quantity, and any drawings or existing battery details. Our engineering team will review your requirements and help define the next steps for your project.

Follow Us: