Where This Build Comes From
Every step in this article comes from one source video — HBPowerwall’s Creating my single biggest D.I.Y. battery with 2800 18650 cells recovered from used laptop batteries, which has been watched more than 3.4 million times. In the video, Pete takes roughly 2800 18650 cells recovered from used laptop batteries, sorts every one into 50mAh groups, refurbishes them with fresh heat shrink and insulator rings, rebuilds them into packs with cell holders, spot-welds nickel strips and bus bars, and turns the whole lot into a 25kWh home energy storage battery. If you would rather watch the build before reading the breakdown, the video is right here:
Why Recover 18650 Cells From Laptop Batteries?
Used laptop batteries are full of high-quality 18650 cells — usually Japanese and Korean cells from Panasonic, Samsung, Sanyo and LG — that are perfectly usable for stationary storage once their remaining capacity is measured. The economics are compelling: a battery that a recycler would pay cents for becomes, after sorting and testing, part of a 25kWh home battery at a fraction of the cost of new cells. The video’s build targets an extra 25kWh on top of the creator’s existing 40kWh system — several years old and still cycling daily — which is the real-world proof that recycled packs can carry a home load for years.
The catch is the work. Every cell has to be tested, graded and matched, and a 2800-cell build is a marathon, not a weekend project. The creator is open about that: it took roughly twelve months of collecting, processing, testing, filming and editing. The reward is a battery built to a standard no off-the-shelf pack matches — because every single cell inside has been individually measured and placed.
Sorting Cells Into 50mAh Groups
The foundation of the whole build is sorting. All 2800 cells are tested for capacity and sorted into 50mAh groups — 2300mAh, 2350mAh, 2400mAh, 2450mAh, 2500mAh, and so on up through 2600mAh and higher — with low and high sub-groups within each band. The video shows the finished layout: rows of bins labelled 23 low, 24 low, 24 high, 25 low, 25 high, 26 low, 26 high and beyond. This is the single most important step in a recycled-cell build, because a pack is only as strong as its weakest cell: if one cell in a series string is significantly lower in capacity, it hits empty first and the whole pack is dragged down with it.
The build then pulls cells from these groups in a deliberate pattern — taking one from the highest group, one from the lowest, and working through the middle — so that every pack gets an even distribution of capacities. This averages out the cell-to-cell differences inside each pack and gives every pack roughly the same performance, instead of stacking all the best cells in one pack and all the worst in another.
Cell Holders and Balanced Pack Building
Each pack is built into a plastic cell holder — in this case, holders that take several cells arranged in series and parallel. The video shows the packing logic clearly: six cells go in as placeholders (marked in blue as not-connected blanks), then the real cells are inserted row by row, and cells from the bottom row are removed and set aside because that row holds the lowest-quality cells — a nice touch of quality control at the assembly stage. Everything not up to standard is pulled out and recycled.
Before cells go into the holders, each one gets fresh heat shrink. The creator runs a utility knife down the old shrink from the positive end to the negative end, lifts it off with a fingernail, and carefully preserves the small white neoprene insulator under the stock heat shrink. New shrink slides on, the insulator rings go back in place over the positive terminal, and a moment of heat makes everything neat and consistent. The cells that were already in good grey shrink are kept; anything else is rewrapped so the whole pack looks uniform.
Bus Bars and Spot Welding
Connecting the cells inside each holder uses the standard 18650 technique: nickel strip spot welding. The video shows the prep work that separates a tidy build from a messy one — the little green centre cap covering each positive terminal is removed to expose a clean welding surface, and a template for the bus bars is marked out using an empty cell holder and a row of nails driven into the bench. The bus bars themselves are made from 10mm² (7 gauge) wire — the kind used for earth wire in Australian homes — stripped, twisted a little tighter with a power drill, and shaped to span the packs.
Thick copper bus bars between packs are what let a 25kWh battery deliver serious current without hot spots, and they are worth copying even in smaller builds. The same wire used for earth in a house is rated for exactly this duty, and twisting it with a drill removes the strands’ natural spring so the bar holds its shape during assembly. If the wire is not perfectly straight after twisting, the creator reverses the drill direction briefly, then spins forward again.
Testing and Quality Control Before Assembly
Quality control runs through every stage of the build, not just at the end. Every cell is capacity-tested before sorting — that is how the 50mAh groups are made in the first place. Cells are re-checked at assembly, and anything that is not great is pulled out and set aside rather than allowed into a pack. Insulator rings are added as an extra layer of protection before the nickel strips go on, so the positive cans cannot short against the strips. And the packs are built with the low-capacity cells deliberately excluded from the duty positions.
This is the real answer to the question people always ask about recycled cells — “aren’t they dangerous?” A used 18650 is dangerous only when its health is unknown. The video’s process — test every cell, grade every cell, match every cell, insulate every terminal — is exactly how you make a recycled pack as safe as a new one. The remaining risk is mechanical: shorting a positive can against a negative strip, which is why the insulator rings and careful welding layout matter so much.
From Cells to a 25kWh Home Battery
The end result of the build is the creator’s single biggest battery yet — around 25kWh of additional home storage, on top of the 40kWh already in service. At typical Australian household draw, that is the difference between running the house through the evening on solar and pulling from the grid at peak rates. The creator is honest about the timeline — collecting the cells alone took months, and the build was filmed over about a year — and he notes in the comments that the pack still sits partly unfinished while his older battery keeps doing daily cycles.
The scale of the build is also the point: 2800 cells is what a serious DIY powerwall looks like, and seeing them all assembled is why the video has 3.4 million views. You do not need to build 25kWh to benefit from the method. The same sorting, matching and welding discipline scales down to a single 4S pack for a caravan, a shed or a small solar system — and the care per cell is identical.
Safety Rules for Recycled Cell Builds
Recycled 18650 builds deserve extra caution, and the video’s habits are the safety rules. First, test every cell for capacity and self-discharge before assembly — unknown cells are the danger. Second, match cells tightly by capacity, because a weak cell in a series string is a fire risk waiting for an unbalanced charge. Third, insulate every positive terminal before welding or fitting bus bars, so a slip cannot short a can against a strip. Fourth, use a BMS with cell balancing on every pack, and fuse the output. Fifth, keep the final battery in a ventilated, non-flammable enclosure — even the best-matched pack deserves a metal box.
One viewer’s question in the comments is the one everyone thinks about: what happens if you accidentally short it? The creator’s answer is characteristically blunt — dead-short it and video it, a million likes — but the serious point underneath is that a 25kWh pack has enormous instantaneous current capacity, so the fuse and the BMS are not optional. Shorts happen in milliseconds; protection has to be already in place.
If you would rather buy a professionally built battery than spend a year recovering cells, that is exactly what we make. 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. Whether you build from recycled cells or buy a ready pack, the same rule applies: know what is inside, and protect it properly.
What Viewers Are Asking (Top Comments on the Video)
Where the creator replied, we quote his answer verbatim; where he didn’t, we give our own practical answer — the way we’d answer a customer on the shop floor. We kept only comments with real practical value and dropped the pure thank-you notes.
Source video: HBPowerwall — “Creating my single biggest D.I.Y. battery with 2800 18650 cells recovered from used laptop batteries” (youtube.com/watch?v=PenPYwa00CA). Comment excerpts are quoted verbatim from the video’s top comments; creator replies are quoted where they exist, and unanswered threads carry Dajiu Energy’s own answers. 3.4M+ views. 2800 used 18650 cells, sorted into 50mAh groups and rebuilt into a 25kWh home energy storage battery.