how to make a 12v 18650 battery pack

How to Make a 12v 18650 Battery Pack from Scratch

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Making your own custom 12v 18650 lithium-ion battery pack may sound intimidating. But I’m going to walk you through the entire process, step-by-step.

Whether you want to create a compact 12v battery to power your latest DIY project or need to replace an old SLA battery, building your own 18650 pack is surprisingly straightforward.

In this guide, you’ll learn things like:

  • How to calculate the number of 18650 cells needed
  • Choosing the right 18650 cells
  • Battery holder options
  • Wiring configurations
  • Adding a BMS (battery management system)
  • Charging and discharging your new battery

And a whole lot more.

So strap on your safety goggles and let’s get to work!

how to make a 12v 18650 battery pack

Why Make Your Own 12v Battery Pack?

Before we dive in, you may be wondering — why go through the trouble of piecing together your own 12v lithium-ion battery?

Here are the main reasons DIYers build their own packs:

Save Money

Pre-built 12v lithium batteries can cost anywhere from $100 to $300+.

By sourcing individual 18650 cells and a basic holder, you can craft a custom battery for a fraction of the cost.

Custom Specs

When you buy an off-the-shelf 12v SLA battery, it likely won’t match your exact voltage and capacity needs.

But with a DIY 18650 pack, you get to dictate the voltage, capacity, discharge rate and more.

Compact Size & Weight

A 12v 5Ah 18650 battery pack takes up far less space than an equivalent lead-acid brick. And it’s many times lighter.

Perfect when size and weight are a concern (like for portable battery boxes, drones, robotics projects, etc).

Reusability

Once an SLA battery dies, that’s usually the end of the road. But with a custom 18650 pack, you can replace worn-out cells down the line and keep on going.

Ok, with the benefits covered, let’s start prepping for our battery build!

How to Make a 12v 18650 Battery Pack?

Step 1: Calculate Number of Cells For 12v

The foundation of any DIY lithium-ion battery is the individual 18650 cells.

So before we worry about wiring configurations or battery protection, we first need to know how many cells are required for our 12v pack.

Here is the simple formula:

Total voltage ÷ Cell voltage = Number of cells in series

Now let’s plug in the numbers.

The standard voltage range of an 18650 cell is:

  • 3.6v (Nominal)
  • 4.2v (Max charge)
  • 2.5v (Discharge cutoff)

For a 12v battery pack, we’ll use the nominal 3.6v figure for our calculation:

12v ÷ 3.6v = 3.33

Rounding up gives us 4 cells in series.

However, we can squeeze a bit more capacity out of our battery by running 3 cells in series (for approx 10.8v). This gives us some cushion before the battery management system cuts off power completely.

So the verdict is…3 lithium-ion cells wired in series gives us the voltage we need.

Now time to source our 18650s!

Step 2: Choosing Quality 18650 Cells

Not all lithium-ion cells are created equal.

The 18650 battery market is flooded with ultra-cheap cells that seem like a good bargain. But trust me, these low-quality cells will cause you nothing but headaches.

Instead, you want high-performing cells from top brands like:

Samsung

Samsung makes some of the best lithium-ion cells on the planet. Their bright green 18650s are my #1 pick.

The Samsung INR18650 35E is a very popular choice that balances performance and cost.

LG

Known for powerful vaping batteries, LG’s 18650 lineup doesn’t disappoint.

The LG MH1 offers a solid 3,000 mAh capacity.

Sony

You can always count on Sony for reliable tech. And their VTC 18650 batteries deliver.

I’m a fan of the Sony VTC6 cell — with its high 30 amp limit and 3,000 mAh rating.

Stick with one of those major brands and you’ll be off to a great start.

Now let’s move onto the next step…

Step 3: Get an 18650 Battery Holder

Once you have your 18650 cells, you need something to physically connect them.

You have two options here:

Spot Welding Nickel Strips

Spot welding involves using a specialized welding machine to fuse thin nickel strips onto the positive and negative terminals of an 18650 cell.

This creates an ultra-secure connection. But the welding gear costs $200+.

Using a Plastic Battery Holder

For most DIYers, a plastic 18650 battery holder is the way to go.

These holders slot multiple cells together and have spring-loaded ends to keep tension on the cell. Two wires with a JST connector then plug into the terminals of the first and last cells.

I like these holders because they’re idiot-proof. No advanced soldering skills needed!

You can grab quality 18650 holders for under $10 on Amazon or sites like Banggood. Just ensure your holder matches the number of cells needed (in our case, 3 cells in series).

Step 4: Wire Cells in Series

To achieve 12v (or close to it), the cells must be connected end-to-end in a series configuration.

This chains them together so the voltage adds up.

Here is how to arrange the cells:

Cell 1 positive terminal faces up and negative terminal faces down.

Cell 2 positive terminal faces down and negative terminal faces up.

Cell 3 positive terminal faces up and negative terminal faces down.

Once slotted into the plastic holder, the cells automatically connect end-to-end.

Those spring terminals ensure a snug fit.

Then you simply attach the red and black holder wires to your project and you now have ~12v DC power!

But before you get charging, there’s an important safety step…

Step 5: Install a BMS

A battery management system (BMS) is crucial when building lithium-ion battery packs from bare 18650 cells.

Here are a few critical jobs a BMS performs:

  • Prevents over-discharging cells
  • Stops overcharging
  • Balances all cells to the same voltage
  • Cuts off if cell temperature gets too high

Without a BMS in place, lithium-ion batteries can be extremely dangerous. They can overheat, catch fire or even explode.

No BMS means no safety. I cannot stress this enough.

Thankfully, small BMS circuit boards designed for 3-4 cell packs are inexpensive (around $5).

To connect it, you simply attach wiring from the BMS to the positive and negative terminals of the first and last cell.

Most BMS will also need a small balance lead attached. But the wiring diagram on the PCB makes installation straightforward.

Now let’s go over how to use and care for your new DIY battery masterpiece.

Charging & Discharging Tips

Charging and discharging properly is key to getting the most life from your homebrew 12v pack.

Here are some quick usage guidelines:

  • Use a Li-ion charger – CC/CV is ideal to maximize cycle count. Charging via solar controller also works.
  • Don’t discharge too low – Stay above 2.5v per cell minimum. The BMS will likely cut-off around this point anyway.
  • Monitor cell voltages – Occasionally check each cell voltage to confirm they’re balancing properly.
  • Keep cool – Heat kills batteries! Don’t enclose tightly and avoid high current draws.

And there you have it — everything you need to know to create your very own 12v lithium-ion powerhouse!

While it takes some specialized parts and electronics knowledge, piecing together a custom battery pack isn’t as hard as it seems.

The effort is well worth it to end up with an ultra-light, high-performance, reusable 12v battery.

Now it’s your turn. Grab some 18650 cells and start building!

make your own 18650 battery pack

How to Make Your Own 18650 Battery Pack

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Making your own 18650 battery pack may seem intimidating, but it’s actually a straightforward DIY project if you have the right parts, tools, and knowledge. In this comprehensive guide, as a professional 18650 battery pack manufacturer, I’ll walk you through everything you need to know to assemble your own powerful and versatile lithium-ion battery.

make your own 18650 battery pack

Why Make Your Own Battery Pack?

Before we dive in, you might be wondering why you’d want to build an 18650 pack instead of just buying one. Here are some of the key benefits:

Cost Savings – Making your own pack from individual 18650 cells is much cheaper than buying a pre-built pack of the same capacity. Savings of 50% or more are common.

Customization – You can choose the exact number of cells wired in series and parallel to achieve your desired voltage, capacity, discharge rate, and physical size. It’s like Lego for batteries!

Recycling – An easy way to source 18650’s is to salvage them from old laptop batteries destined for landfills. Giving these cells a second life is great for the environment.

Education – Building your own pack is an enlightening hands-on learning experience about lithium battery tech. You’ll gain practical skills and may even find a new hobby.

How to Make Your Own 18650 Battery Pack

What You’ll Need

Building a battery pack takes the right gear and some DIY skills. Here’s an overview of what you’ll need:

Parts

  • 18650 cells
  • Battery holders
  • Nickel strip
  • Wire
  • Connectors
  • BMS (battery protection circuit)
  • Insulators and wraps

Tools

  • Multimetre
  • Spot welder (or soldering iron)
  • Hot glue gun
  • Wire cutters/strippers
  • Heat gun
  • Safety gear (gloves, glasses)

I’ll go over each of these parts in more detail throughout the article so you know exactly what to get.

Choose 18650 Cells

At the core of every 18650 pack are – you guessed it – 18650 battery cells. But there are tons of different options for lithium-ion cells on the market:

Battery Cell Formats

The most common Li-ion cell sizes you’ll encounter are:

  • 18xxx (18650, 18700, etc.)
  • 26xxx
  • 21700

Cell Chemistries

Variations in the cathode chemistry impact the performance of lithium cells:

  • NMC (Nickel Manganese Cobalt Oxide)
  • NCA (Nickel Cobalt Aluminum Oxide)
  • LFP (Lithium Iron Phosphate)

Specifications

The key specs to consider are:

  • Nominal voltage (3.6-3.7V is normal)
  • Capacity (mAh rating)
  • Maximum continuous discharge rate (amps)

My default recommendation for a budget but dependable cell is the Samsung 25R 18650. This NMC cell offers a great balance of capacity, current handling, and safety at a reasonable cost. LG, Sony, Panasonic and Sanyo also make excellent cells.

Calculate Battery Config

Once you’ve chosen your cells, the next step is figuring out how to wire them together into a pack. This comes down to understanding series and parallel connections.

Battery Connections

Series connections add voltage.

Parallel connections add capacity and discharge current.

With 18650 packs we wire cells into parallel groups first. Then connect those groups together in series to achieve the target pack voltage.

For example, a “3S2P” pack means 3 parallel groups of 2 cells wired in series.

Configuration Math

Let’s design a 12V 10Ah pack from Samsung 25R cells (3.6V, 2500mAh):

Target voltage = 12V

Target capacity = 10Ah (or 10,000mAh)

Single cell specs:

  • Voltage (nominal) = 3.6V
  • Capacity = 2500mAh

Configuration:

Number of cells in series: 12V / 3.6V per cell = 3 cells in series

Number of parallel groups:
10000mAh target capacity / 2500mAh per cell = 4 cells in parallel

Our pack needs 3 parallel groups of 4 cells wired in series = 3S4P

So we need a total of 3 x 4 = 12 18650 cells

Assemble 18650 Cell Holders

A clean and safe way to assemble Li-ion packs is using plastic 18650 cell holders. These holders snap together to keep the cells neatly aligned and spaced. They allow good airflow for cooling while also preventing shorts.

Arrange the holders to match your planned 3S4P layout. Make sure the cell orientation alternates so positive and negative terminals line up. Hot glue the holders together if desired.

Then insert your cells and connect them with…

Battery Wiring Options

You need to make electrical connections between cells to complete the circuit. Here are two options:

Spot Welding Nickel Strip

Spot welding uses a powerful impulse of current to melt nickel strips to cell terminals. It makes strong reliable joints without introducing much heat into the cell.

You’ll need:

  • Spot welder (~$250 for entry level machine)
  • Pure nickel strip
  • Bench power supply

Procedure:

  1. Cut strips of nickel
  2. Set welder heat and duration
  3. Weld strips BETWEEN groups first
  4. Then weld each GROUP in parallel
  5. Insulate welds with fish paper

It takes practice to make good consistent welds. Start with scrap cells first.

Soldering Cells

You can solder cells together but it takes a very gentle touch. Too much heat can damage the cell internals.

Supplies needed:

  • High wattage soldering iron
  • Thick pure copper wire or braid
  • Lead-free rosin core solder
  • Lots of flux

Steps:

  1. Clean cell end and wire/braid surface
  2. Apply generous flux
  3. Heat and melt solder so it flows onto joint
  4. Hold just long enough for solder to flow
  5. Avoid directly heating cell more than a couple seconds!

Take precautions not to overheat the cell or breathe fumes when soldering.

Add a BMS

No 18650 battery pack is complete without a BMS, or battery management system. This crucial protection circuit monitors all cells in the pack and prevents:

  • Over-charging
  • Over-discharging
  • Short circuits
  • Over current
  • Cell imbalance

So a BMS really helps ensure safe, reliable operation of your DIY lithium pack.

Choosing a BMS requires matching:

  • Number of cells (12S, 10S, etc)
  • Maximum current rating (for motor, inverter loads)
  • With or without a charging port

Solder the balance wires to nickel strips between groups, cable tie them in place. Connect discharge wires to the first and last cell. Consult the diagram included with your BMS for proper wiring.

Enclose and Protect Pack

Nearly done! To complete your power-packed battery, it’s important to insulate and protect the cells and wiring from bumps or moisture:

Insulate exposed metal with fish paper and Kapton tape

Structurally support cells with foam padding

Electrically isolate BMS and terminals

Fuse discharge wires to protect from short circuits

Wrap entire pack in insulating plastic

Contain in an enclosure or battery box

For a streamlined finish, apply warning labels for voltage, polarity and capacity. Add an power switch, charging port and mounting hardware.

Initial Testing

Before powering up your creation, do some final safety checks:

  • Confirm appropriate polarity of all wired connections
  • Verify insulation everywhere
  • Measure and record individual group voltages
  • Watch initial charge cycle for problems
  • Only use a proper CC/CV lithium charger

If all goes well, you now have a robust homebrew 18650 pack to power projects for years to come! Building your own is deeply satisfying, plus the skills you’ve learned are handy for assembling all kinds of battery-powered devices.

Hope you’ve found this DIY 18650 battery guide useful – let me know if you have any other Li-ion battery questions!