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48V Off-Grid ESS · NEXUS + APEX-6.5K · Indoor System
This system pairs one BigBattery NEXUS 14.3kWh battery with one APEX-6.5K hybrid inverter into a single closed-loop off-grid setup — 14.3kWh of storage and 6,500W of continuous output, with two separate AC inputs so grid and generator can stay connected at the same time. It's an indoor installation for both components, built for cabins, homesteads, and off-grid homes, and it scales up to 214.5kWh on the same platform if you need more later.
Two components, pre-matched and sold together.
Qty 1
Floor-standing 48V LiFePO₄ battery, expandable up to 15 units in parallel for 214.5kWh total.
Qty 1
6,500W continuous output with two separate AC inputs for simultaneous grid and generator connection.
LiFePO₄ storage rated for 6,000+ cycles, with a 7.6kW continuous power rating and 270A peak discharge for 1 second.
The APEX-6.5K delivers 6,500W continuously with headroom to start motors and pumps without tripping.
Two separate AC inputs mean grid and generator can both stay wired in at once, with solar charging independently on top.
Two independent MPPT trackers pull up to 10,000W combined, adjusting continuously through the day.
Up to 15 NEXUS units can run in parallel on the same platform, for serious long-term capacity growth.
Routes up to 80A straight to critical loads — enough to carry a well pump or HVAC run without staging separate circuits.
The NEXUS battery is rated for years of daily charge and discharge cycles before capacity meaningfully declines.
Multi-layer protection on both the battery and inverter for safe, reliable day-to-day operation.
Rather than picking a battery and inverter separately and hoping they communicate well together, this system ships as one closed-loop pairing: the NEXUS battery and APEX-6.5K inverter are designed and sold to work with each other directly. The APEX-6.5K's two independent AC inputs mean grid and generator can both stay connected simultaneously rather than switching between them, while solar charges through its own dual-MPPT circuit — a genuine differentiator from single-AC-input inverters like BigBattery's own APEX-10K.
Worth knowing before installing: this is an indoor system on both sides. The NEXUS battery is IP54-rated and specified for indoor, floor-standing installation — not the outdoor/all-weather rating some other BigBattery batteries carry — and the APEX-6.5K is IP20, also indoor-only. Plan for a garage, utility room, or dedicated power space rather than an outdoor enclosure. In exchange, the platform scales seriously: up to 15 NEXUS units can run in parallel for 214.5kWh of total storage, well beyond what a single unit provides.
Battery — BigBattery NEXUS 14.3kWh (×1)
| System voltage | 48 V |
| Nominal voltage | 51.2 V |
| Chemistry | LiFePO₄ |
| Usable energy | 14.3 kWh |
| Ah capacity | 280 Ah |
| Cell configuration | 16S1P |
| Max continuous discharge current | 140 A |
| Max continuous power | 7.6 kW |
| Max discharge peak current | 270A (1 sec) |
| Max charge current | 140 A |
| Charging voltage range | 53.5–57.6 V |
| Charge temp range | 32–113°F |
| Discharge temp range | -4–113°F |
| Optimal discharge temp | 59–95°F |
| Humidity range | 10–95%, no condensation |
| Protection rating | IP54, indoor floor-standing |
| Weight | ~315 lbs |
| Dimensions (W×H×D) | 19.7 × 27.5 × 15.7 in |
| Communications | RS485, RJ45, CAN |
| Max connections | 15 parallel (214.5kWh) |
Inverter — APEX-6.5K (×1)
| Rated output power | 6,500 W |
| Max output (surge) | 13,000 VA |
| Output voltage | 120/240 Vac split-phase |
| Motor load capacity | 4 HP |
| Switching time | 10 ms (typ.) |
| MPPT channels | 2 (1+1) |
| Max solar input power | 5,000W + 5,000W |
| Max solar charge current | 140 A |
| MPPT tracking efficiency | 93% |
| AC inputs | 2, grid + generator (simultaneous) |
| Bypass overload current | 40 A |
| Pass-through capacity | 80 A |
| Dimensions | 25.51 × 16.14 × 5.51 in |
| Weight | 48 lbs |
| Protection rating | IP20, indoor only |
| Parallel capacity | Up to 6 units, 3-phase at 3+ |
Certifications: UL1741, RoHS, FCC Part 15 Class B, IEC62109-1/2.
This same NEXUS and APEX-6.5K platform is sold in several sizes. The row below highlighted in your brand color is the configuration this page describes — everything else is shown for reference if a customer needs a different scale.
| Tier | Inverters | Batteries | Capacity | Max Output |
|---|---|---|---|---|
| Standard | 1× | 1× | 14.3 kWh | 6.5 kW |
| Standard | 1× | 2× | 28.6 kWh | 6.5 kW |
| Standard | 1× | 3× | 42.9 kWh | 6.5 kW |
| Large | 2× | 2× | 28.6 kWh | 13 kW |
| 3-Phase | 3× | 3× | 42.9 kWh | 19.5 kW |
One BigBattery NEXUS 14.3kWh battery and one APEX-6.5K hybrid inverter, sold as a pre-matched closed-loop pair — 14.3kWh of storage and 6,500W of continuous output.
No — both components are indoor-rated. The NEXUS battery is IP54 and specified as indoor floor-standing, and the APEX-6.5K inverter is IP20. Plan for a garage, utility room, or dedicated indoor power space.
Solar and one AC source at a time — but the APEX-6.5K's two separate AC inputs mean grid and generator can both stay wired in simultaneously, with solar charging independently on its own circuit. That's different from single-AC-input inverters, which can only use grid or generator, not both together.
It depends on your total connected load. At 6,500W continuous (13,000VA surge) it covers most efficient homes and cabins, but a full load calculation is worth doing before sizing your system — especially with well pumps, electric heat, or several large appliances running together.
Yes — up to 15 NEXUS battery units can run in parallel for 214.5kWh of total capacity, and additional APEX-6.5K inverters can be paralleled up to 6 units (3+ forming a three-phase output) for more power.
The NEXUS battery carries a 12-year manufacturer's warranty and the APEX-6.5K inverter carries a 5-year manufacturer's warranty — two separate coverage periods for the two components.
Given the voltages and currents involved, installation should be handled by a qualified, licensed electrician or solar installer familiar with your local code requirements.
Battery — BigBattery NEXUS
Inverter — APEX-6.5K
Free shipping on all orders within the mainland US (Hawaii, Alaska and overseas territories excluded - a freight forwarder is required). Orders ship directly from our brand partners' warehouses across the U.S. Order confirmation is emailed immediately; if an item is unexpectedly backordered we notify you before your card is charged. In-stock items are processed within 1-4 business days (cut-off 4:00 PM EST), transit is 3-6 business days, and tracking is emailed within 24 hours of shipment. Typical delivery is 4-10 business days from purchase. Minimum order value is $69.
You have 30 days from the delivery date to initiate a return (35 days for orders placed Nov 25-30 and Dec 25-31). Items must be unused, in original packaging with tags attached, and returns require prior authorization from our team.
To start a return: +1 (307) 317-7213, hello@ecosolarkits.com, or live chat. Read the full return and refund policy
