Where This Guide Comes From
Every figure and step in this article comes from one source video — Dan from Freely Roaming assembling a 12V 280Ah LiFePO4 battery with four EVE prismatic cells and a 120A BMS, watched more than 280,000 times. He builds the pack on camera, shows the wiring order, reads the cell voltages, and walks through the BMS app. If you would rather watch the build before reading the breakdown, the video is right here:
The video answers a question that gets more relevant every year as store-bought lithium prices fall: is it still worth building your own LiFePO4 battery? Dan's answer, backed by his own capacity tests, is that a DIY 280Ah pack still lands around 18 cents per watt-hour, against roughly 28 cents for the cheapest commercial units — about 35% cheaper, while adding features like low-temperature cutoff and Bluetooth monitoring. Below is the full breakdown, every number taken from the on-camera build.
Why Build Your Own 280Ah Pack in 2026?
Commercial prices have dropped hard — you can find 100Ah LiFePO4 batteries around $350, and Dan has reviewed several of them on his channel. So why bother assembling cells at all? The video gives four reasons that still hold. First, cost per watt-hour: his 280Ah pack costs about 18 cents/Wh, versus 28 cents/Wh for the cheapest shelf battery. Second, size: four 280Ah cells occupy roughly the footprint of a 100Ah pack — almost triple the capacity in a comparable box before the enclosure. Third, component choice: you pick the BMS, the cells and the busbars yourself, so you get exactly the protection and current rating your system needs. Fourth, serviceability: build it yourself and you know how to repair it, replace a cell or swap a BMS when the time comes.
That logic is familiar territory for anyone shopping in our product center — choosing between a finished drop-in pack and a custom build is a real decision, and it depends on your budget, your time and how much risk you want to manage. The same cost-per-Wh thinking shows up across our battery guides.
The Parts List: Cells, BMS and Hardware
The build uses four 3.2V 280Ah LiFePO4 prismatic cells — the LF280K model, widely associated with EVE production — each reading 3.29V open-circuit with 0.21 milliohm internal resistance, shipped by Shenzhen Qishou Tech. Dan points out one detail worth checking on any prismatic cell: his cells came with laser-welded studs instead of threaded terminals, which removes the classic failure mode of stripped threads and over-tightened bolts penetrating the terminal base.
Protection comes from a Radio B Tech 120A BMS (about $120 on Amazon) — the same unit behind brands like Current Connected and Overkill Solar. It ships with a Bluetooth dongle, two (actually three) temperature sensors, 10-gauge flexible silicone wires for the main negative, and fully programmable protection parameters. The bundle also includes busbars with oval holes (so they can slide on the studs) and serrated flange nuts — Dan swaps those for plain nuts and washers because the flange nuts are too large for his BMS lugs.
Prep Work: Cell Balancing Before Assembly
Before any build, the cells must be at the same state of charge. The video explains the honest version of this: you can do a top balance — connect all four cells in parallel (all positives together, all negatives together) and let them sit for five to ten days to equalize, then charge to full. The reason balancing is hard to eyeball is that a LiFePO4 voltage curve is flat in the middle — the only places where voltage clearly reflects state of charge are the very top and the very bottom. So the reliable way to know four cells match is either a parallel rest, or careful measurement at the extremes.
For a first build, this step decides everything downstream. Matched cells mean the BMS sense wires see consistent voltages, the balance function starts close to done, and no single cell gets hammered during cycling.
Assembling the 4S Pack: Orientation and Strapping
The mechanical assembly is deliberately beginner-friendly. The four cells are oriented positive, negative, positive, negative to make the series (4S) connection. Dan inserts a thin plastic sheet between cells — he cuts 50-59 folders from Target into cell-sized sheets — to add insulation in case a wrapper chafes. He then straps the cells into two pairs with strapping tape, and straps the pairs together, which holds the middle cells better than a single wrap around all four.
Busbars go on in order: positive, negative, positive, negative — four connections across the cells, with the main positive and main negative at opposite ends of the pack. The point of the oval holes becomes obvious here: the bars can slide slightly on the studs as the cells swell and contract during cycling, which is normal LiFePO4 behavior and should never be locked rigid if you can avoid it.
Wiring the BMS Sense Leads Correctly
This is the part that trips up most builders, and the video shows it step by step. The BMS sense leads are color-coded: the first red wire goes to cell 1 positive (the main positive), then each subsequent wire lands on the next cell negative in order. The last connection is the main negative, where the BMS's three blue 10-gauge wires also terminate — that combined point becomes the pack's negative output. The BMS's B- terminal connects to the battery negative; C- becomes the system negative for the whole pack.
One subtle detail worth copying: Dan does not trim the sense wires. Each wire carries a tiny voltage drop proportional to its length, so keeping all sense wires the same length keeps the BMS's voltage readings consistent across cells. If you cut one short and leave another long, the BMS reads slightly different voltages that are an artifact of wiring, not cell state.
Temperature Sensors and the Low-Temperature Cutoff
The Radio B Tech BMS ships with three temperature sensors; the video mounts one near the bottom of the pack and one near the top. Taped to the cell sides, they feed the BMS's low-temperature disconnect — if the pack gets too cold to charge safely, the BMS blocks charging rather than letting lithium plate inside the cells. For anyone running batteries in a van, boat or unheated garage, that single feature is worth a lot: charging LiFePO4 below about 0°C is one of the fastest ways to permanently damage cells.
Dan also flags a real thermal caveat of his build: the BMS is taped directly to the side of the pack, and a BMS heats up under load, so that heat can transfer into the adjacent cells and accelerate their degradation. In a permanent install, mount the BMS away from the cells with airflow — an enclosure with the BMS on a bracket is the clean way to do it.
Verifying the Pack: Voltage Readings and the BMS App
With everything finger-tight, the proof is a multimeter. Dan reads 13.11V across the main terminals, and per-cell: 3.27V, 3.27V, 3.26V, 3.27V — four cells within a hundredth of a volt of each other, which is exactly what a freshly equalized 4S pack should show. Then he connects the BMS to the XiaoXiang app over Bluetooth and walks through the dashboard: capacity, temperature from all three sensors, total voltage with a graph, power in/out, and fault status showing "none."
The app's programmability is powerful — and the video warns it is dangerous for beginners. Under parameter settings, presets for LiFePO4 4S normal and light pre-populate common protection values. The "light" profile drops some settings to more conservative numbers to extend battery life, but if you use it, your charger must be programmed to match the lower charge voltages. For most users, the normal preset is the right starting point, and it still exposes every parameter for those who know what they are doing.
The Cost Math: 18 Cents per Watt-Hour
The headline number in the video: this 280Ah pack works out to 18 cents per watt-hour, versus about 28 cents/Wh for the cheapest commercial LiFePO4 available — a ~35% saving with low-temp cutoff and Bluetooth included. At 12.8V nominal, 280Ah is roughly 3.58kWh, so the under-$700 build delivers capacity that would cost well over $1,000 from most retail brands. Dan notes the pack has no enclosure, terminals or fuse in its basic form — those are additions you supply, and a fuse and breaker are explicitly recommended for safety, especially in any mobile or vibrating environment.
If that math appeals to you but soldering and BMS wiring are not your idea of a weekend, the same capacity is available as a finished pack — and that is exactly the choice we help customers make at Dajiu Energy, whether they want a ready-made drop-in battery or a custom pack engineered to their voltage and size.
Safety Notes Every Builder Should Respect
Dan opens and closes the video with the same warning, and it deserves to be repeated: building a battery pack is a potentially dangerous project. A mistake can start a fire, cause an explosion, or injure you severely — especially in a mobile environment with vibration. Specific rules from the build: fuse the pack even though the demonstration skips it, keep insulation sheets between cells, mount the BMS where its heat cannot soak into cells, respect the low-temperature cutoff, and never charge a damaged or swollen cell. If you are not confident, buy a commercial pack instead — that is a legitimate and often smarter choice.
We say the same to customers every week: DIY lithium is a great path when you have the skills and the time, and a finished pack is a great path when you do not. Both are valid, and both are options we can support — from single drop-in units to OEM volumes. More of that reasoning is in our battery guides.
And if you're not hunting for a consumer brand but need the battery itself — a custom LiFePO4 pack at a specific voltage and capacity, an OEM or ODM project, or wholesale supply for your own power station 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.
What Viewers Are Asking (Top Comments on the Video)
These are the most useful of the video's top comments, with our practical answers. The creator pinned his own comment with the buying details; where he answered a question, we quote him directly, and where he did not, the answer below is ours. Thanks-only comments were left out on purpose; these are the ones with actual information in them.
Source video: Freely Roaming — "EASIEST DIY 12-Volt 280Ah LiFePO4 Battery // Step-By-Step Build" (youtube.com/watch?v=TjrtqBTlO6w). Comment excerpts are quoted verbatim from the video's top comments; the creator's pinned comment is quoted directly, and where the creator did not reply, all answers are Dajiu Energy's own. Build figures are transcribed from the video's measurements.