Every figure in this article comes from one source video — byte sized engineering's How To Make A Lithium Battery Pack With 18650 Cells, watched more than 609,000 times. Hosted by engineer Zach, the video walks through making a 48V 10Ah lithium battery pack from 52 ordinary 18650 cells: holding them in modular clips, wiring a 13S4P arrangement, spot welding nickel strips, soldering balance leads, adding a battery management system and insulating the finished pack — then testing it in a real OneWheel. If you would rather watch the build before reading the breakdown, the video is right here:
The video answers a question every maker asks at some point: is it possible to build your own battery pack, and is it even cost-effective? The numbers are concrete — the commercial 48V 20Ah pack used in the project cost about $340, roughly half the entire build budget. The DIY 10Ah pack that replaces it comes out to about half of that. Along the way the host shows exactly why the 18650 cell is everywhere — from laptop batteries to Teslas — and why safety habits like voltage matching, spot welding and a proper BMS are non-negotiable. Below is the full breakdown, every number taken from the build. These are the same fundamentals behind every pack we assemble at Dajiu Energy.
The video opens with a practical question: is building your own battery pack possible, and is it even cost-effective? The host's real example makes the stakes clear. His DIY electric OneWheel project used a purchased 48V 20Ah battery pack that cost about $340 — roughly half of the entire project budget, charger included. That experience is what pushed him to learn how to build packs himself. The short answer the video lands on: yes, you can build one safely if you understand electronics and follow the process carefully — and for makers who build more than one project, the cost and flexibility pay off quickly.
That same economics question is why we publish breakdowns like this at Dajiu Energy. Understanding what is inside a battery pack — how cells are connected, how protection works, what "48V 20Ah" actually means — is the best foundation for choosing between a DIY build and a factory-built lithium battery pack that arrives certified and warrantied.
For this build the host uses the most common lithium cell in the world: the 18650. The name is simply the dimensions — 18mm in diameter and 65mm long. These cells are everywhere: laptop batteries, drill batteries and even Tesla electric vehicles. Each cell in the build is rated 3.7V nominal and 2,500mAh capacity.
Like any AA or AAA battery, each 18650 has a positive and a negative terminal — the difference is they are less obvious, marked on the cell wrapper rather than as a raised button. Getting the orientation right matters more than it does with alkaline cells: connect one backwards in a series chain and the result is a short, then heat, then fire. The host's first rule is to keep the markings straight and double-check every placement.
To reach 48V from 3.7V cells, the host connects 13 cells in series. Voltage adds in series, capacity adds in parallel — so one string of 13 cells gives 48V but only 2.5Ah. To get useful capacity he builds four parallel strings of 13 cells — a 13S4P pack — for 48V at 10Ah, about half the capacity of the commercial pack in his OneWheel.
Holding 52 cells in the right orientation is a real challenge, and the video uses modular battery clips designed for 18650 cells. The holders snap together, so you can build the grid to whatever size and shape your project needs — here, a 13-by-4 grid with the cells alternating direction so series connections can be made simply by bridging the gap at each end, snake-style from bottom to top.
The electrical connections are made with nickel strips and a spot welder, not solder. Spot welding passes a brief, high-current pulse through two tips to weld the nickel to the cell terminal — the weld is solid and the heat pulse is so short it barely warms the cell. Soldering, by contrast, applies prolonged heat that can damage the internals of a lithium cell, and it creates dry-joint risks on the small contact area.
The host uses a cheap battery-powered spot welder from Amazon. He is candid that it is a budget tool — fine for hobby builds, while professional-quality units are the right call for serious or production work. The nickel strip itself comes in a wide format that makes series welding faster, cut into pieces sized to each gap. Before welding, he checks voltages at each node and confirms the expected values — a habit that catches a wrong orientation before it becomes a fire.
A raw 48V pack of cells is not safe to charge or discharge on its own. The build adds a battery management system (BMS), which provides over-discharge and over-voltage protection and — critically — balances the cells so every series group stays at the same voltage during charging. The BMS connects to each series node with balance leads.
One detail the video gets right: the balance leads are soldered to the pack before the last nickel tab is welded, so the soldering iron never touches a cell directly. Soldering heat into a lithium cell is exactly what you want to avoid, and this ordering trick keeps the heat away from the cells entirely. The host wires a thick 10AWG cable for discharge — the path that carries real current to the load — and a lighter cable for charging, since charge current is lower. An XT60 connector handles discharge and a Deans connector handles charging, the same standard used on his OneWheel.
With all cells welded and the BMS installed, the pack needs physical and electrical insulation. The host wraps the pack in a rubber cabinet-liner sheet bought from a hardware store — roughly $8 for a big roll, far cheaper and thicker than craft foam. The liner keeps the cells protected from vibration, prevents shorts against the enclosure and provides a cushion layer around the pack. A final blue heat-shrink wrap gives the pack a professional, finished look and adds another layer of mechanical protection.
Insulation matters for a simple reason: a single scrape through a cell wrapper, touching the aluminum case of another cell, creates a short that can dump the whole pack's energy through a tiny contact. That is why factory-built packs — like our LiFePO4 drop-in replacement batteries — use proper separators, insulating layers and sealed enclosures, tested before they ship.
The build ends with the real test: the pack is installed in the OneWheel and ridden. The voltage meter reads 35% state of charge when first connected — expected, because cells are not shipped fully charged for safety — and once the footpad is pressed and the rider leans forward, the OneWheel moves. The pack works.
Beyond "it works," the host notes a less obvious win: confidence and reuse. Once you have built one pack, you can build more for future projects at the cost of cells and materials, sized to whatever voltage and capacity you need. That is the maker advantage — and it is the same logic behind custom OEM/ODM packs for products that need a specific voltage, shape and capacity at scale.
The video closes with honest math. Building the same 48V 20Ah spec as the purchased pack would cost about $270 in parts versus $340 retail — roughly 20% savings. That saving comes with real costs of its own: the time to build, the spot welder and materials, and the responsibility for safety. The host's conclusion is practical: if you only ever need one battery, buying is usually the smarter move; if your projects need lots of different packs, investing in the tools and skills to build your own pays off.
That trade-off applies on both ends of the market. For a one-off personal build, the DIY route can save money. For anything that powers a product you sell, or that runs unattended — an RV, a home backup, a commercial system — the warranty, certifications and consistency of a factory-built battery pack are usually worth more than the 20% difference. It is the same decision we help customers weigh every week.
For a skilled maker with multiple projects, this build saves about 20% per pack and delivers exactly the voltage and capacity you need. But it takes time, a spot welder, careful cell handling — and full responsibility for the result. For one-off or safety-critical use, a factory-built lithium battery pack gets the same capability tested, warranted and certified. The real value of this video is knowledge: understanding series and parallel, spot welding, balance leads and BMS protection is exactly what lets you judge the quality of any battery product you buy. If you need the power without the DIY time, a custom LiFePO4 pack engineered to your voltage and capacity is what we do every day.
And if you're not hunting for a consumer brand but need the battery itself — a custom pack at a specific voltage and capacity, an OEM or ODM project, or wholesale supply for your own product line — that's what we do. Dajiu Energy is a Chinese manufacturer building LiFePO4 batteries for RVs, homes, golf carts and portable applications since 2017. Our product range covers LiFePO4 drop-in replacement batteries, EV and golf cart batteries, wall-mounted home storage, portable power stations, commercial energy storage and battery swap cabinets — explore the full lineup in our product center, or browse more buying guides. Tell us your voltage, capacity and size, and we'll engineer the pack to hit it.
These are the most useful of the video's top comments, with our practical answers. The creator did not reply to these threads, so all answers below are ours — written the way we'd answer a customer on the shop floor. Thanks-only comments were left out on purpose; these are the ones with actual technical value.
Source video: byte sized engineering — "How To Make A Lithium Battery Pack With 18650 Cells" (youtube.com/watch?v=3dD5KmM8ciU). Comment excerpts are quoted verbatim from the video's top comments; the creator did not reply to these threads, so all answers are Dajiu Energy's own. Build figures are transcribed from the video.
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