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A 4S DIY battery kit for 314Ah-class cells: the same case family as our 280Ah kit, a smart BMS and the full accessory set for MB31-class prismatic LiFePO4 cells — supplied as a kit, assembled by you, branded by you.
Why a Separate 314Ah Page for the Same Case?
Because buyers ask for it by name — and because the honest answer is more useful than a second size table. 314Ah prismatic cells (EVE MB31, CATL 314Ah, Hithium 314Ah) share the same footprint family as the 280Ah class: roughly 174 mm long, about 72 mm thick, about 207 mm tall including terminals. Case makers rate the same boxes across both capacities — an established maker’s official 12V kit page states the fit plainly as “280–314Ah”. So this kit uses the same case family, the same accessory set and the same size range as the 12.8V 280Ah kit. We do not publish a second, different set of “314Ah case dimensions”, because in the real market there isn’t one — any listing that implies a special 314Ah-only box should be asked what physically differs.
What the 314Ah cells themselves change is energy: four in series give a nominal 12.8V pack of about 4.0 kWh instead of 3.6 kWh — roughly 12% more runtime in the same locker, the same rack space and the same mounting footprint. For RV, marine and off-grid product lines sold by capacity, that is a real range-topping variant, not a relabel.
The kit is supplied in three tiers. The market uses loose words like “complete kit” for all three, so we define each tier by what is physically in the box:
| Tier | What is in the box | What you supply |
|---|---|---|
| 1 — Case-only kit | Case plus accessory set: series busbars, sampling board or balance harness, insulation set, main terminals, protection hardware, fasteners | Your cells and your own BMS |
| 2 — Case + BMS kit (standard offer) | Everything in Tier 1, plus a fitted 4S smart BMS. This is the configuration meant when a listing says “Battery Case + BMS + Accessories (Cells Not Included)” | Your cells |
| 3 — Complete kit with cells | Everything in Tier 2, plus 4 matched Grade A 314Ah cells of the model confirmed in your order | Assembly only |
If you only need the protection board itself, see our standalone smart BMS boards. If you would rather not assemble at all, finished units are in our 12V LiFePO4 battery range and surveyed in the 12V LiFePO4 battery series guide.
Reference Standard Configuration
The table below is the reference build most buyers start from. Dimensions are the shared 280/314 case-family range — identical to the 280Ah kit page, deliberately.
| Item | Reference configuration | Basis |
|---|---|---|
| Pack format | 4S (4 × 3.2V cells), 12.8V nominal; ≈4.0 kWh with 314Ah cells | Fixed by the kit design |
| Case format | Powder-coated steel case; sealed ABS waterproof case as the light-duty option — the same case family as the 280Ah kit | Option — see matrix below |
| Case size, reference range | ≈ 342–402 × 185–230 × 247–273 mm — the shared 280/314 case-family range, not a separate 314Ah size set | Reference range — exact drawing confirmed per order |
| Cell layout | Single row of 4 cells (row ≈ 288 mm thick at the cell faces), with compression plates | Fixed by the kit design |
| BMS (Tier 2/3) | 4S smart BMS, 200A continuous class, Bluetooth monitoring; 100A class for lighter-duty builds | Brand family and model confirmed per order |
| Main protection | Fuse or breaker sized to the BMS class | Rating and type per kit — confirmed per configuration |
| Display | LCD or touch display on some with-BMS configurations; not included in the case-only tier | Per kit — confirmed per order |
| Main terminals | P+ / P− terminal pair sized to the current class | Confirmed per configuration |
Configuration Options — Nothing Is Locked
| Dimension | Options | Notes |
|---|---|---|
| Supply tier | Case-only / Case + BMS / Case + BMS + cells | See tier table above |
| Case format | Steel case; sealed ABS waterproof case; custom dimensions for volume programmes | Custom sizes are an OEM item, confirmed per project |
| Cells fitted (Tier 3) | EVE MB31, CATL 314Ah, Hithium 314Ah | Terminal form confirmed against the physical batch |
| 280Ah fallback | The same kit accepts the full 280Ah-class family (LF280K and equivalents) | One case platform covers both variants of your product line — see the 280Ah kit page |
| BMS family | JK (active balancing, Bluetooth built in) / JBD (passive balancing, Bluetooth module, RS485 and heating options) / Daly (classic passive lines, or the active-balance line) | Category options — the brand and model in your kit are confirmed in writing per order, never assumed |
| BMS continuous current | 100A / 120A / 150A / 200A class | Size from your inverter and load profile, not from the cell label |
| Balancing | Active 1A or 2A, or passive balancing depending on BMS family | Active balancing earns its cost on large-format cells |
| Communication | Bluetooth app monitoring as the norm; RS485 as an option module; CAN is a custom item at 4S, not a standard fit | Say so in the enquiry if a system controller needs a wired link |
| Display | LCD / small touch display / none | “None” applies to the case-only tier |
| Heating pads | Optional add-on | Not standard fit. Add them if the pack will charge below 0 °C; this is separate from BMS low-temperature charge protection |
| OEM appearance | Case colour, your logo and labels, rating plate, manual and packaging | See the OEM / ODM section |
Cell Compatibility: The 314Ah Models, Verified Against the Footprint
314Ah is a capacity class, not a mechanical standard — what makes these cells fit is that the major makers kept the 280-class envelope when they raised capacity. The three widely available 314Ah models:
| Cell | Capacity | Size (L × T × H, mm) | Terminals |
|---|---|---|---|
| EVE MB31 | 314Ah | 173.7 × 71.7 × 207.2 (incl. terminals) | Factory flat terminals for laser welding; DIY-market versions with M6 or double-thread M6 welded studs |
| CATL 314Ah | 314Ah | 174.26 × 71.65 × 207.2 (incl. terminals) | M6 laser-welded stud |
| Hithium 314Ah | 314Ah | 174.7 × 71.65 × 207.11 | M6 stud (DIY-market version) |
| 280Ah-class family (for reference) | 280Ah | 173.7–174.7 × 71.55–72.0 × 207.1–207.5 | M6 stud versions; REPT terminal form varies by source |
The compatibility rule is mechanical, not commercial: a cell fits if its footprint falls inside the family above and its terminal form matches the busbar drilling. Note the EVE MB31 line in particular — the same cell reaches the DIY market with plain flat terminals or with welded M6 studs depending on channel, and those need different busbar hardware. Send the exact cell model and its terminal version with your enquiry and the match is confirmed in writing. If you are still choosing cells, our guide on choosing LiFePO4 cells for pack assembly and the 280Ah / 314Ah prismatic cell range are the right starting points; cells are also listed on our cell wholesale page.
What Is in the Accessory Set
- 3 copper series busbars — a 4S pack needs one link per cell junction, i.e. series count minus one; the count follows the format, not a marketing bundle
- BMS connection busbar set — the main-path links between cell block, BMS and terminals (a separate set from the series links)
- Sampling board, or a balance-wire harness — the two market forms of the same job: routing the 5 sense taps (B0–B4) to the BMS in order
- P+ / P− main terminals, sized to the current class
- Fuse or breaker for the main path, rating per kit configuration
- Display where the confirmed kit includes one
- Insulation set — epoxy / fibre sheets between cells and case, EVA pads between cells
- Fastener pack — terminal bolts, case and lid screws
Exact counts of insulation pieces and fasteners follow the bill of materials of the case in your order and are listed in the order confirmation — makers vary these counts widely, and we would rather confirm ours in writing than copy a competitor’s packing list.
Assembly: Four 314Ah Cells Into a Working 12.8V Pack
- Check the cells before anything is bolted. Compare resting voltage and internal resistance across all 4 cells, and bring them to a common state of charge. On MB31-class cells, also verify which terminal version you actually received — flat or stud — before the busbars come out of the bag.
- Insulate first. Epoxy or fibre sheets between the cell block and the case, separators between cells. In a steel case especially, prismatic cell cans must never rely on the cell’s own film alone.
- Set the row under even compression. Fit the end plates snugly and evenly — prismatic LFP cells want moderate, uniform compression, not maximum force. Torque values come from the cell maker’s manual for your exact cell model and are stated in the kit documentation; there is no universal number, and anyone who gives you one without naming the cell is guessing.
- Land the sampling connections before the power path. Fit the sampling board or balance harness from B0 upward and verify every tap reads in sequence before any busbar carries current.
- Bolt the series busbars in order — 3 links, polarity checked twice. Work cell 1 negative to cell 2 positive and onward, checking polarity at every step with a meter, not by eye.
- Wire the BMS main path and protection. B− to the first cell’s negative, P− out to the load terminal, fuse or breaker in the main line, then the P+ terminal. Confirm the BMS wakes and reads all 4 cell voltages before the lid goes on.
- Supervise the first full cycle. Watch per-cell voltages on the app or display through the first charge — on a 4.0 kWh pack the first cycle takes longer than the 280Ah build, and patience here is what separates a matched pack from a warranty return.
- Close up and record the build. Note the cell batch, BMS model and settings on the build sheet. That record is what makes warranty discussions and repeat orders simple.
A necessary word on who should do this: a 12.8V 314Ah pack can deliver very high fault currents despite its modest voltage. Assembly belongs with trained technicians using insulated tools. If your operation does not have them, buy the finished battery instead — it is the honest recommendation.
Where a 4.0 kWh DIY Pack Earns Its Keep
- Range-topping RV and camper models — the same locker space as a 280Ah build with about 12% more usable runtime, sold as the premium variant of an existing 12V line; see our RV power page
- Marine house banks — sailing and workboat house power where one larger pack means one less parallel unit to wire and balance; see marine power
- Small off-grid and cabin systems — longer autonomy between generator runs on 12V-native loads; see off-grid power
- Assembler product lines — one case platform, two capacity variants: kit commonality keeps case inventory single while the catalogue offers both 280Ah and 314Ah finished packs
OEM / ODM: Your Brand, Your Specification
The kit format exists for buyers who sell under their own name. OEM options cover case colour, logo and rating labels, manuals and packaging; configuration options cover the BMS family and current class, terminal arrangement, display, and — on Tier 3 — the cell model the kit is built around. For volume programmes, case dimensions can be produced to a project specification rather than taken from the standard range.
Our role in that process is coordination: requirements are confirmed in a written specification, matched against manufacturing partners’ production, and the agreed checkpoints and documents are handled on the export side. The specification confirmed in your order document is what binds the shipment — not this web page, which is why every variable item above is marked “confirmed per order”. Start from our OEM & ODM coordination page or the OEM / ODM RFQ checklist if you want the full document list.
What to Send Us for a Quotation
- Tier — case-only, case + BMS, or complete with cells
- Cell model and terminal version — the exact 314Ah cells you will fit, flat-terminal or stud version (or ask us to supply them under Tier 3)
- BMS current class and main loads — inverter size and surge loads, so the current class is confirmed against your real use, not the cell label
- Case format — steel or ABS, and any dimensional constraint of the locker, rack or compartment it must fit
- Quantity and destination — a sample kit for evaluation, or your expected regular volume, plus the destination port
One logistics advantage worth planning around: Tiers 1 and 2 contain no cells, so they ship as general cargo — no lithium-battery dangerous-goods freight. Many buyers ship kits by standard freight and source cells on a separate, optimised route; Tier 3 ships as regulated lithium cargo like any cell shipment. Exact packing dimensions and weights for your configuration are stated in the quotation.
Related reading before you enquire: the BMS selection guide for sizing the board, and the rest of this series below.
Frequently Asked Questions
Is there a dedicated 314Ah case I should be looking for?
For 12V, essentially no — and that is the point of this page. The 314Ah cells kept the 280-class footprint, so the established kit makers rate one case for both (an official 12V kit page states the fit as “280–314Ah”). A seller presenting a special 314Ah-only case at a premium should be able to name a physical difference; if the answer is a different sticker, buy the shared case.
What do I actually gain over the 280Ah kit?
About 0.4 kWh more nameplate energy — 4.0 kWh against 3.6 kWh — in the identical footprint, mounting and case inventory. The gain is runtime and a higher-capacity variant for your catalogue, not a different product platform. Everything else — BMS classes, accessory set, assembly — is the same discipline as the 280Ah build.
Can I mix 280Ah and 314Ah cells in one pack?
No. Cells in a series string must be the same model and batch class; mixing capacities guarantees the smaller cells are over-worked at both ends of every cycle while the BMS sees only the string average per tap. Build 280Ah packs or 314Ah packs — the kit supports both, the string must not.
Does the MB31’s terminal version matter?
Yes, more than any other detail on this page. EVE MB31 reaches the market as a flat-terminal cell for laser welding and as a DIY version with welded M6 (single or double-thread) studs. The busbars, torque and hardware differ. State which version your cells are when you enquire; if you are buying cells and kit together under Tier 3, we confirm the pairing in the order specification.
Do I have to buy the BMS from you?
No. Tier 1 is case-only precisely for buyers with their own BMS platform. What we would ask is which board you plan to fit: the case’s BMS mounting position and display cut-out are arranged around a board class, and it is cheaper to confirm that fit on paper than to discover it on the bench.
Is a heating pad included?
No — heating pads are an optional add-on, confirmed per order, and we say so plainly because some listings imply otherwise. Add them if the finished pack will be charged below 0 °C. They are a different thing from the BMS’s low-temperature charge cut-off, which is a protection setting on the board itself.
The DIY Kit Series
This page is the 12.8V 314Ah model in an eight-model DIY kit series: 12.8V 100Ah / 280Ah / 314Ah (4S), 25.6V 280Ah / 314Ah (8S), and 51.2V 100Ah / 280Ah / 314Ah (16S). Each model gets its own page because the cases, cell families and assembly details genuinely differ. The other seven models in the series: the 12.8V 280Ah DIY kit, the 12.8V 100Ah DIY kit, the 25.6V 314Ah DIY kit, the 25.6V 280Ah DIY kit, the 51.2V 314Ah DIY kit, the 51.2V 280Ah DIY kit and the 51.2V 100Ah DIY kit. The full product range is on Products.
Request a quotation for this kit: Start a DIY-Kit-12V314 inquiry · WhatsApp: +86 159 8945 0735
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