Where This Build Guide Comes From
Every step in this article comes from one source video — Offgrid Power Solutions’ Very Detailed Beginners Guide To Building A Custom DIY LiFePO4 Battery, which has been watched more than 157,000 times. In the video, the builder takes four EVE 280Ah prismatic cells, top-balances them, compresses them between plywood end plates with threaded rods, wires up a 200A Daly smart BMS and assembles a complete custom 12V 280Ah pack inside a wooden case. The video runs nearly 80 minutes because every detail — torque figures, cable sizes, balance-lead order, even how to drill the end plates — is shown on camera. If you would rather watch the build before reading the breakdown, the video is right here:
Why Build a Custom 280Ah LiFePO4 Pack?
A custom build exists for one reason: the finished pack in the video is roughly 210mm wide by 326mm long by 330mm high — a shape that is not a standard off-the-shelf size. If you need a battery that fits an odd compartment, or a capacity that no drop-in unit offers at your price, building from prismatic cells gives you complete freedom over the footprint. The trade-off is spelled out honestly in the video: the moment you change the case dimensions, you also change the bus bar lengths and the wiring route, so a custom pack is not a shortcut — it is a build, and it should be planned on paper first.
That said, a standard direct-replacement size exists for this class too: roughly 185mm by 370mm by 250mm is the box that most 12V 200–300Ah drop-in batteries use. The video’s build deliberately goes custom — wider, taller and shorter — to fit the owner’s space, and the whole point of following the guide is that you can scale the same method to whatever dimensions your install demands, as long as you re-check the wiring geometry when you do.
Cell Selection: Four EVE 280Ah Prismatic Cells
The heart of the pack is four EVE 280Ah prismatic cells, each measuring about 72mm by 175mm by 200mm. Prismatic cells are the right choice for a large DIY bank: rigid, rectangular, and easy to bolt together with bus bars, unlike cylindrical cells which need spot welding. Four cells in series gives a nominal 12.8V — the same voltage as a lead-acid replacement — and a true 280Ah of capacity, which works out to roughly 3.5kWh of usable energy in a 12V system.
The cells arrive at about 25% to 30% state of charge, which is the shipping norm for LiFePO4 — enough to verify voltage without carrying a full charge, and safe for transport. Before anything else, the video checks each cell’s resting voltage and confirms the cells are all close, which is the cheapest form of cell matching. Cells that start far apart force the BMS to work harder and shorten pack life, so a quick voltage check up front is non-negotiable.
Top Balancing Before Assembly
Because the cells start at a similar but not identical state of charge, the build top-balances them before assembly. The method shown in the video is the simple parallel-charge approach: all four cells are connected in parallel — positive to positive, negative to negative — using ordinary 1.5mm household wire, and charged together at a fixed 3.65V until the whole bank settles at full charge. With roughly 800Ah in parallel, this takes days rather than hours, and the video is upfront about the wait. The alternative is a bench power supply acting as a balance charger, which runs about 70–80 pounds in the UK market — or a cheap fixed 3.65V charger, which is what many builders use.
Why bother? A pack assembled from cells at slightly different states of charge will rely on the BMS to equalize them after assembly, and the harder the BMS has to work, the more heat and wear it sees. Top balancing takes the cells to the same full-charge point before they ever meet a bus bar, so the BMS starts with four equal cells and only has to handle normal drift. For a 280Ah pack — a lot of energy to babysit — starting balanced is the difference between a maintenance-free bank and one you keep an eye on.
Compression: Threaded Rods and Why Pressure Matters
Prismatic LiFePO4 cells expand slightly when charged and relax when discharged, and controlled compression keeps the internal layers in contact, which slows capacity fade and prevents the pouch from ballooning. The video’s compression system is simple and effective: four M6 threaded rods, 300mm long, running through the plywood end plates, with nuts and washers tightened evenly. The builder’s advice is to keep the rods snug but not brutally tight — the goal is firm, even pressure, and you can re-check and re-tighten after the first few charge cycles as the cells settle.
A useful detail from the video: small pieces of pipe or tube over the threaded rods protect the cell corners from the rod edges and give the compression a neat finish, and the whole assembly sits on the case floor on its side so the rods run horizontally — a layout that keeps the bus bars and BMS on top for easy access. The end plates themselves are 9mm plywood, doubled up, cut to about 215mm wide with a 230mm and 300mm height pairing, which gives the pack a rigid, square face that distributes the rod pressure evenly across the cell faces.
Building the Case
The case is a wooden box, and the video treats it as part of the engineering, not decoration. The plywood is cut so the compressed cell stack fits snugly, the outer panels are painted black for a clean finish, and the lid is removable so the BMS and wiring stay accessible. Holes are drilled at precisely marked positions — 10mm holes for the M6 connection nuts, and matching holes for the cables to pass through — and the builder emphasizes measuring twice before drilling, because a misplaced hole in a 280Ah pack case means drilling again through a stack of live cells.
One commenter on the video adds the obvious safety reminder: when you drill and install the bottom wood plate, be extremely careful not to screw or drill into the battery cells — the plates sit directly against the cells, and a screw that goes through the wood into a cell is a short circuit in the making. The builder confirms the point: plan every hole, mark the drill depth, and never let a fastener wander into the cell stack.
Wiring: Bus Bars, Torque and Cable Sizes
The wiring section is where the video earns its “very detailed” title. The pack is connected in series with bus bars and M6 hardware, and the builder’s rule is short and worth memorizing: fewer connection points is always better, because every connection is a place that generates heat under load. That logic drives two choices: use the longest sensible bus bars to bridge cells directly, and use 2AWG (35mm²) cable for the main battery leads so the high-current path stays cool.
Torque is specified precisely — about 8 N·m on the M6 bus bar connections — and the builder recommends a bicycle torque wrench so you can hit the number consistently. Washers go under the nuts to spread the load, and a clever tip from the video is adding washers under the balance-lead ring terminals too, to stop the leads twisting and pulling loose when you tighten them. Finally, the connection hardware list is practical: M6 threaded rods and nuts, 17mm connection nuts, 8mm and 10mm ring terminals for the main cables, and adhesive heat-shrink to cover the terminal connections once they are torqued.
Installing the Daly Smart BMS
The BMS is a 200A Daly smart BMS in a 4S 12V configuration — the popular choice for this class of pack. The smart version adds a Bluetooth module (about $3 extra) and temperature sensors, so you can read per-cell voltage, state of charge and temperature from your phone, and the BMS handles overcharge, over-discharge, overcurrent and temperature cutoffs automatically. For a 280Ah bank, 200A continuous is a comfortable rating that covers a typical inverter surge without tripping.
The balance-lead wiring order is the one place beginners fail, and the video shows it slowly: the black wire goes to B- (the overall negative), then the four red balance wires connect to the intermediate cell junctions in series order, finishing at B+. Each balance wire is secured with a washer and a flange nut, and the builder’s tip is to route the leads so they cannot twist when the terminals are tightened. If you get the order wrong, the BMS will read nonsense voltages and may refuse to work at all — so label every wire before you start and double-check the sequence against the BMS diagram.
Safety and Practical Tips from the Build
A 280Ah pack stores more than 3.5kWh — enough to do real damage if assembled carelessly — and the video’s details encode the safety rules: top-balance before assembly, torque connections properly, keep every connection point minimal and clean, insulate exposed bus bars and terminals with adhesive heat-shrink, and never work on the pack with rings or metal jewelry on your hands. The comment section of the video adds two legitimate cautions: keep a fire extinguisher nearby when you first charge the pack, and consider separating the cells with thin fish paper or acrylic sheet if the pack will live in a high-vibration environment like a boat — though in most van and RV builds the factory wrap plus compression is sufficient.
One commenter also makes a fair point about BMS choice: Daly was the go-to budget brand when this video was made, but the market has moved on, and builders today have strong alternatives with better apps and balancing current. The builder acknowledges the video is a few years old and newer options are available — which is a good reminder to compare BMS options yourself rather than assuming one brand forever. Whichever BMS you choose, the wiring principles are the same: correct balance-lead order, solid torque, and a BMS rated for your pack’s current.
If you would rather buy a professionally built pack than build your own, a custom 12V 280Ah bank 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. If you do build your own, we’d still suggest matching the video’s care — and if you’d rather not, tell us your voltage, capacity and compartment dimensions and we’ll engineer the pack for you.
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: Offgrid Power Solutions — “Very Detailed Beginners Guide To Building A Custom DIY LiFePO4 Battery” (youtube.com/watch?v=-ZxcGc59M60). 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. 157K+ views. Four EVE 280Ah prismatic cells become a 12V 280Ah pack with a 200A Daly smart BMS, threaded-rod compression and a custom wooden case — every step from top balancing to final wiring.