BigBattery NEXUS 48V 15 kWh LiFePO4 battery paired with APEX 6.5K off-grid inverter

Product Description

This kit pairs one BigBattery NEXUS 48V LiFePO4 battery — 280Ah, 14.3 kWh usable per BigBattery — with the APEX 6.5K all-in-one inverter: 6,500W of continuous split-phase 120/240V output, two MPPT solar inputs rated 5,000W + 5,000W, and built-in battery charging from grid or generator, per BigBattery. BigBattery sells this as an off-grid and backup power system — it runs your loads from battery, solar, or an AC charging source, and it is not sold as a grid-interactive (sell-back) system.

Who This Is For

Cabins, guest houses, seasonal properties, workshops, and defined backup circuits — refrigeration, lighting, pumps, electronics, and 240V appliances at moderate scale. It fits owners whose daily energy use is modest today and who want a single battery cabinet with a clear path to more storage later. If your concern is peak power — large motor starts, several 240V loads at once — look at the APEX 10K version of this kit instead.

Key Features

  • 6,500W continuous split-phase 120/240V output, 13,000VA maximum output, per BigBattery
  • Two MPPT solar inputs, 5,000W + 5,000W (125–450Vdc MPPT range, 18A + 18A), per BigBattery
  • Two AC inputs (grid and generator) — up to 80A grid/generator charging and up to 140A solar charging, per BigBattery
  • NEXUS battery: 280Ah, 14.3 kWh usable, 6,000+ cycle life, self-heating function, aerosol fire suppression, per BigBattery
  • Room to grow: NEXUS parallels up to 15 units and the APEX 6.5K parallels up to 6 units, per BigBattery
  • Inverter certifications: UL1741 / RoHS / EN61000-6-1 / EC61000-6-3 / FCC Part 15 Class B, per BigBattery

Why BigBattery

BigBattery is a US company building LiFePO4 energy storage for off-grid and home backup use; the APEX line is BigBattery's own inverter family, so battery and inverter come from one manufacturer. Kits ship from Texas and are backed by lifetime USA-based technical support, per BigBattery. See our full BigBattery collection.

What's In the Kit

Solar panels, racking, and array wiring are not included — arrays are sized to your site. BigBattery's kit listing does not itemize cables or accessories, so call us at (302) 496-3554 before ordering and we'll confirm exactly what ships with your configuration.

Specifications

Battery 1 × BigBattery NEXUS, 48V class (51.2V nominal), LiFePO4, 280Ah
Usable energy 14.3 kWh, per BigBattery
Battery max continuous discharge 140A (7.6 kW max continuous power), per BigBattery
Battery cycle life 6,000+ cycles, per BigBattery
Battery communications RS485 / RJ45 / CAN
Battery dimensions / weight 19.7 × 27.5 × 15.7 in; approx. 315 lb
Inverter APEX 6.5K — 6,500W rated output, 13,000VA maximum, split-phase 120/240Vac
Solar input Two MPPTs, 5,000W + 5,000W; 125–450Vdc MPPT range; 18A + 18A
Charging Up to 140A from solar; up to 80A from grid/generator; two AC inputs (grid & generator)
Battery voltage range (inverter) 40–60Vdc
Inverter parallel capability Up to 6 units, per BigBattery
Inverter certifications UL1741 / RoHS / EN61000-6-1 / EC61000-6-3 / FCC Part 15 Class B, per BigBattery
Inverter dimensions / weight 25.51 × 16.14 × 5.51 in; 48 lb
Battery warranty 12-Year Limited Warranty, per BigBattery
Inverter warranty 5-Year Limited Warranty, per BigBattery
Kit SKU K0191

Sizing Your Off-Grid Home

Start with energy. Example assumptions — label and adjust for your own loads: refrigerator 1.5 kWh/day, chest freezer 1.0, LED lighting 0.4, well pump 1.0, electronics and internet 1.0, washer 0.5. That totals about 5.4 kWh/day, so 14.3 kWh usable (per BigBattery) covers roughly two such days without sun. Add a mini-split (commonly 5–15 kWh/day in season, depending on size and climate) or electric water heating and you move to cycling the bank daily — that is what the 30–45 kWh version of this kit is for.

Then check power. 6,500W continuous covers a cabin-scale panel — and the battery keeps up: one NEXUS supports up to 140A, about 7.6 kW continuous, per BigBattery, so a single battery can carry this inverter at full rated output.

Installation

Setting the 315 lb battery cabinet and wall-mounting the 48 lb inverter are the easy parts. The AC side — panel interconnection, overcurrent protection, grounding, bonding — belongs to a licensed electrician working to the National Electrical Code (NEC) and local codes, and most jurisdictions require a permit and inspection for energy storage. Place the battery in a dry space kept above freezing; BigBattery's published charge range starts at 32°F.

Warranty & Support

Battery: covered by BigBattery's 12-Year Limited Warranty — in BigBattery's words, “BigBattery, Inc. guarantees that its products will be free from defects in material and workmanship for a period of twelve (12) years.” Included accessories are covered for 1 year, and no registration is needed, per BigBattery. Inverter: the APEX 6.5K is covered by a 5-Year Limited Warranty, per BigBattery.

BigBattery publishes a 30-Day Money Back Guarantee; per BigBattery, non-defective returns are refunded at purchase price minus a 20% restocking fee, excluding shipping. All returns require a Return Merchandise Authorization (RMA) before anything ships back — call OffGrid Horizon at (302) 496-3554 and we'll open the RMA or warranty claim with BigBattery. We're a family-owned authorized BigBattery partner, and BigBattery backs the system with lifetime USA-based technical support.

Shipping

This kit ships as palletized freight within the United States. Inspect the pallet before signing: note any damage on the delivery receipt and contact us promptly — that notation keeps a freight claim simple.

Frequently Asked Questions

Is this a grid-tie system?

No. BigBattery sells it for off-grid and backup power applications. The APEX 6.5K's two AC inputs accept grid or generator power for battery charging, per BigBattery, but the system is not sold as a grid-interactive (sell-back) inverter.

Are solar panels included?

No. The two MPPT inputs accept up to 5,000W + 5,000W of PV per BigBattery; panels and racking are sized to your site and sold separately. The system can also run on battery plus grid/generator charging without solar.

Can I add more storage later?

Yes — NEXUS batteries parallel up to 15 units, per BigBattery. The 2- and 3-battery versions of this kit are listed separately if you already know you need more.

Will it start motors and 240V equipment?

BigBattery rates the APEX 6.5K at 13,000VA maximum output for short-duration demands above its 6,500W continuous rating. For a specific well pump, compressor, or shop tool, call us with the nameplate figures and we'll talk it through.

Do I need an electrician?

Yes — the AC interconnection, grounding, and code compliance are work for a licensed electrician, and most jurisdictions require a permit and inspection.

How does the battery handle cold weather?

Per BigBattery, the NEXUS discharges from −4°F to 113°F and charges from 32°F to 113°F, with a self-heating function. Install it in a space that stays above freezing for dependable winter charging.

Not sure between the 6.5K and the 10K? Call OffGrid Horizon at (302) 496-3554 — we're a family-owned authorized BigBattery partner and we'll size it with you honestly.

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