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Full Guide to Customize 18650 Battery Pack

How To Customize 18650 Battery Pack

This article can show you what you need to consider when customizing your 18650 battery pack, making it easier for you to DIY your 18650 battery pack.
Let’s read it together!

What is an 18650 Battery?

18650 battery cell is named for its 18mm diameter and 65mm height, it’s larger than an AA battery. 18650 battery pack is a good choice for diverse applications like laptops, drones, power tools, and medical devices.

As an experienced battery expert, we have more than 15 years of experience in 18650 lithium-ion battery manufacturing.

In this post, you’re going to learn exactly how to customize the 18650 battery pack you need step by step.

How are 18650 Cells Different From Other Batteries?

Normally, 18650 lithium-ion batteries have a higher voltage, requiring fewer cells in series for suitable electronics applications, and lower internal resistance means there is not much energy loss.

18650 Battery Cells

And what makes 18650 so popular is that they have an impressive power density.

A single 18650 cell can store from 3wh to 13wh and also

has a large density, ranging from 100 to 265 watt-hours per kilogram, which makes them an excellent choice for high-power battery packs such as power tools lithium batteries, and electric motorcycle bikes.

Assessing The Configuration and Number of Cells Needed for an 18650 Battery Pack.

To create the desired battery pack, it’s essential to determine the required voltage, capacity, and charge/discharge current.

Connecting the 18650 battery in series will increase the voltage of the battery pack, and parallel connections will increase the battery pack capacity.

So the first step is to assess the configuration and number of cells needed for the 18650 battery pack. Different applications usually have different specifications and requirements.

For example, E-bike batteries typically operate within the 36 to 72-volt range, while consumer electronics applications can be configured for 12, 24, 48-volt systems, or any voltage in between.

18650 Battery Pack

Determining Series Configuration

Numerous 18650 battery packs are often designed using a mix of series (S) and parallel (P) connections.

In the case of laptop batteries with an 11.1V 4.8Ah battery pack, it typically involves arranging three 3.7V 18650 battery cells in series (3S) to achieve a nominal 11.1V.

Additionally, two cells are connected in parallel (2P) to enhance the capacity from 2.4Ah to 4.8Ah. This specific configuration is referred to as 3S2P, indicating three cells in series and two in parallel.

Series Connection of Four Cells

How Many 18650 Batteries to Make a 48v Battery?

For a 48-volt battery using 18650 cells, assemble approximately 13 cells in series, each with a nominal voltage of 3.7 volts.

Ensure the cells have similar capacities and come from a reliable source. Connect the positive terminal of one cell to the negative of the next, and consider adding a protection circuit for safety.

To achieve 48 volts, you can calculate the number of cells needed as follows:

Number of Cells = Desired Voltage / Nominal Voltage per Cell

For a 48-volt battery using 3.7-volt cells:

Number of Cells = 48 V / 3.7 V ≈ 13 cells

So, you would need around 13 cells in series. Please note that for lithium ion batteries (NMC batteries), the fully charged voltage is 4.2 volts, and the nominal voltage is 3.7 volts.

Determining Parallel Configuration

If you need the battery pack to reach 13.6ah capacity, it means that it needs 13600/ 3400= 4 parallel according to the parallel connection to increase the capacity, For a 18650 3400mah battery, need 4 parallel to reach the 13600mah of the battery pack.

Parallel Connection of Four Cells

Customize 18650 Battery Pack

Determine the Load Current: Initiate the process by determining the load current, denoting the amount of current essential for the device powered by the battery pack.

This determination is crucial as it dictates the gauge of wires and components necessary to manage the current, along with specifying the number of cells needed to fulfill the required current.

Calculate the Capacity: Subsequently, calculate the capacity of the battery pack, indicating the stored energy. This calculation involves multiplying the load current by the desired runtime of the device.

Select the Cells: Once the load current and capacity are established, select cells capable of meeting these criteria.

It’s vital to opt for cells with a discharge rate adequate to match the load current and a capacity sufficient to meet the desired runtime.

Determine Cell Quantity: Based on the load current and capacity, ascertain the number of cells required to fulfill the specifications.

To compute the cell quantity, divide the desired capacity by the capacity of a single parallel group cell.

Customize 18650 Battery Pack

Customize 18650 Battery Pack

1. Screening of lithium battery cells
Screening of 18650 battery cell voltage, internal resistance, and capacity, also known as the capacitance distribution group, to ensure that the voltage difference within 5mV, internal resistance difference within 3mΩ

2. Combine the cells in series and parallel
When assembling the battery to install the battery cell bracket, between the battery cells have a battery bracket the battery heat dissipation and good, can better avoid the damage caused by vibration.
3. Spot welding of the battery pack
The materials used for spot welding are pure nickel and nickel-plated steel strips, pure nickel’s internal resistance is small, has stronger overcurrent capability, and is less prone to rust.
The nickel-plated steel strip has a larger internal resistance, poor overcurrent capability, and is more prone to rust. The nickel tape is controlled between 0.1 – 0.2mm.

4. Welding protection plate for battery pack
Use a lithium battery protection plate, the welding of the protection plate needs to be welded according to the specification of the protection plate, and wiring definition diagram.

5. Insulation packing and shaping of battery packs
Insulate and pack the battery pack, fix the battery pack wires to prevent water and dust from entering, and better protect the lithium battery pack.

6. Installation of the battery pack into the housing
Need to connect the exposed wires of the battery pack to the shell connector of the shell, including the charge and discharge terminals, fuses, switches, and so on.

7. Finally, test the lithium battery pack
Including lithium battery charging and discharging cycle tests, capacity tests, internal resistance tests, open circuit voltage tests, over-current tests, over-charging tests, over-discharging tests, short circuit tests, and so on.

The reasons for several problems to be understood in the assembly of 18650 lithium battery packs:

  • Why use the protection plate: the protection plate can control the charging and discharging of the battery to ensure that the battery will not be overcharged or over-discharged resulting in battery fire or explosion.
  • Voltage, capacity, internal resistance control: voltage error is too large, then the cell with high voltage will automatically charge the cell with low voltage.
    Too large an error in internal resistance will lead to unbalanced heating of the battery cells and an unbalanced energization rate.
    The capacity error is too large, resulting in the over-discharge of some cells. These factors on the 18650 lithium battery pack life decline, and vice versa can enhance the use of efficiency and life;
  • The core to ensure that not mixed: new and old battery cells can not be mixed, so ensure that the core is for the same batch of cells.

How to calculate how many cells are needed for a set of lithium batteries?

To produce a 64V-25AH lithium battery pack, using a nominal voltage of 3.2V, and a capacity of 2.5AH lithium iron phosphate 18650 cells, how many cells are needed?

  • Number of strings:64V÷3.2V=20 strings
  • Number of parallels: 25AH ÷ 2.5AH = 10 and
  • Total number of cells: 20*10=200pcs

To produce a 74V battery pack with a total capacity of about 3.7 kWh, how many 3.7V-50AH square-case cells are needed to meet the demand?

  • Capacity: 3700wh÷74v=50AH
  • Number of strings: 74v ÷ 3.7v = 20 strings
  • Total number of cells:20*1=20pcs

A few suggestions for assembling lithium batteries

  1. Cell selection: 3.2V lithium iron phosphate, 3.7V lithium ternary, this is a simple distinction.The battery cell is divided into many levels, with capacity, and power model distinctions.The difference involved is the discharge rate, the theory is that the higher the discharge rate, the better, but the power battery also has a high school and low distinction.Good batteries are prioritized to supply electric vehicles and screened down to flow into the market, the market will be screened again by large merchants, good for battery packs, poor into the retail market.How to distinguish between good and bad batteries?You must use the internal resistance tester and power test. Test how much MH is nominal and how much MH is actual; if the gap is bigger from the nominal parameter, it means the quality is worse.

    The lower the battery’s internal resistance, the better, routinely below 50.

  2. Treatment of battery cells: Use an internal resistance tester to test the voltage, internal resistance, and capacity of the batteries one by one, put the cells together if they are the same, and let them stand for 7~15 days, and then test them again if they are still the same, then they can be assembled.
  3. Battery spot welding: Artificial spot welding is not recommended. Battery spot welding strength control is not reasonable, the battery point is through liquid leakage, the nickel sheet point is not virtual solid welding, artificial soldering iron welding, and the solder temperature is too high, which will hurt the pole piece.
  4. Environmental issues: Battery packs should be waterproof and shockproof and provide heat conduction channels to prevent corrosion.
  5. Protection plate selection: According to their motor power to judge the choice, to ensure that the voltage matches, and to achieve high-capacity small power use.
  6. Charger selection: According to the protection board, the protection voltage should match, and according to the capacity to choose the appropriate A/H charger, the charger should also pay attention to the waterproof and shockproof protection.

Applications of 18650 batteries

18650 Battery for Vape

The 18650 battery is a rechargeable lithium-ion battery commonly utilized in vape mods due to its recharging capability and higher energy capacity than alternative battery types.

A quality 18650 vape mod battery typically features a specified “amp limit,” indicating the maximum power it can deliver without overheating or risking explosion (ideally surpassing 30A).

18650 Battery for Vape

18650 for an Electric Bike Battery

Battery packs consist of individual battery “cells,” which fall into two main categories: cylindrical cells, akin to AA and AAA batteries, and prismatic cells, found in devices like phones.

Within each class, batteries are produced in various form factors, referring to their size in the battery industry. The widely adopted form factor for cells in an e-bike battery pack is the 18650.

18650 Battery for Electric Bike


18650 lithium batteries known for their unique size and efficiency, play a crucial role in the shift to electric power.

I hope this post showed what you need to consider when customizing your 18650 battery pack, whats the 18650 difference compared with other battery cells?

If you have any ideas or comments about the Customize 18650 Battery Pack, please feel free to contact us.


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