Product Description

The BigBattery APEX 6.5K is an all-in-one off-grid inverter for 48V battery banks: a 6,500W split-phase 120/240V pure sine wave inverter, dual MPPT solar charge controllers, and a grid/generator battery charger in one indoor-rated unit. Per BigBattery, it runs closed-loop with the NEXUS, ETHOS, and HUSKY 2 INV battery platforms. OffGrid Horizon is a family-owned authorized BigBattery partner serving customers across the US.

Who This Is For

Cabins, small off-grid homes, guest houses, and essential-loads backup where 6,500W of continuous output covers the load list. Split-phase 120/240V output means it can feed a standard US panel, including 240V circuits such as well pumps. If your plans include heavier simultaneous loads, compare the APEX 10K.

Key Features

  • 6,500W rated output / 13,000VA maximum, split-phase 120/240Vac pure sine wave, per BigBattery
  • Dual MPPT solar input — 5,000W per tracker (10,000W total), 125–450Vdc MPPT range, 550Vdc max open-circuit voltage, 18A max input per tracker
  • Built-in charging — up to 140A from solar, 80A from grid or generator, 140A max hybrid charge current
  • Two AC inputs (grid and generator) with 10ms typical switching time
  • Closed-loop battery communications — RS485 / CAN / USB / dry contact; per BigBattery, compatible with NEXUS, ETHOS, and HUSKY 2 INV, with an optional Wi-Fi module for monitoring
  • Parallel up to 6 units; per BigBattery, three or more can form three-phase output
  • UL1741 listed, plus FCC Part 15 Class B, RoHS, EN61000-6-1, IEC62109-1/-2, per BigBattery

Why BigBattery

BigBattery is a US-based company known for its LiFePO4 battery platforms; the APEX line is its matching 48V off-grid inverter family, designed so battery and inverter share data out of the box. Per BigBattery, APEX inverters carry a 5-year warranty with Lifetime USA-Based Tech Support.

Specifications

Rated output power 6,500W
Max output power 13,000VA
Output 120/240Vac single/split-phase, pure sine wave, 50/60Hz
Battery voltage 48V nominal (40–60Vdc range)
MPPT trackers 2 (1 + 1)
Max PV input power 5,000W + 5,000W
MPPT voltage range 125–450Vdc
Max PV open-circuit voltage 550Vdc per tracker
Max PV input current 18A + 18A
Max solar charging current 140A
Max grid/generator charging current 80A
AC inputs 2 (grid and generator)
Switching time 10ms (typical)
Communication RS485 / CAN / USB / dry contact; optional Wi-Fi module
Parallel capability Up to 6 units
Noise Under 60dB
Operating temperature 14°F to 131°F (derates above 113°F)
Protection IP20, indoor only
Dimensions 25.51 x 16.14 x 5.51 in
Weight 48 lb
Certifications UL1741, FCC Part 15 Class B, RoHS, EN61000-6-1, IEC62109-1/-2
Warranty 5 years, as published by BigBattery
SKU INV034

All specifications per BigBattery's published product page and spec sheet.

What It Runs

The figures below are planning estimates only — actual wattage varies by model, so check appliance nameplates and confirm with your installer. Keep total running watts under the 6,500W rating, and keep motor-start surges within the 13,000VA maximum, per BigBattery.

  • Refrigerator: roughly 150–400W running
  • Chest freezer: roughly 100–350W running
  • 1 HP well pump (240V): roughly 1,000–1,500W running, with a start surge of 2–3 times that
  • Microwave: roughly 1,000–1,500W while cooking
  • Small mini-split or window AC: roughly 500–1,500W running
  • Lights and electronics: roughly 200–500W

Example (estimate): refrigerator 300W + freezer 200W + well pump 1,200W + mini-split 1,000W + lights and electronics 400W is about 3,100W running — within the 6,500W rating, with headroom left for pump starts.

Installation

The APEX 6.5K is IP20 rated for indoor installation only — a garage, utility room, or similar protected space. Keep PV strings inside the 125–450Vdc MPPT window and never above 550Vdc open-circuit, including cold-weather voltage rise. Connecting the output to a distribution panel involves grounding, bonding, permits, and local code — use a licensed electrician. Run the battery communication cable per BigBattery's manual for closed-loop operation with compatible 48V batteries.

Warranty & Support

Per BigBattery, the APEX 6.5K carries a 5-year warranty with Lifetime USA-Based Tech Support. As a family-owned authorized BigBattery partner, OffGrid Horizon can help with setup questions, troubleshooting, and claims. Returns require a Return Merchandise Authorization (RMA) — contact us before shipping anything back. Call (302) 496-3554.

Shipping

Ships within the United States. The unit weighs 48 lb and travels in protective packaging; please inspect the carton on delivery, note any damage with the carrier, and contact us right away so we can make it right.

Frequently Asked Questions

Is this a grid-tie inverter?

No. BigBattery sells the APEX 6.5K as an off-grid inverter: its AC inputs use grid or generator power for charging and pass-through, and BigBattery's materials do not describe exporting power to the grid.

Does it need solar to work?

No — it can run from the battery bank alone and charge from grid or generator power. Solar panels connect to the built-in MPPT inputs when you add them.

Which batteries pair with it?

Per BigBattery, it runs closed-loop with the NEXUS 48V (15 kWh), ETHOS, and 48V HUSKY 2 INV platforms, plus certain EG4 models. Size the bank so its continuous discharge rating covers your planned loads.

How much solar can I connect?

Per BigBattery: up to 5,000W per MPPT tracker (10,000W total), with strings inside the 125–450Vdc operating window and below 550Vdc open-circuit.

Can I expand later?

Yes — per BigBattery, up to 6 units can be paralleled, and three or more can form three-phase output.

Will it run 240V appliances?

Yes — output is split-phase 120/240V, so it can feed 240V circuits such as well pumps and dryers, provided total load stays within its ratings.

Is the 10ms switching time fast enough for computers?

BigBattery publishes a 10ms typical switching time. Many electronics ride through that; for critical equipment, a small UPS downstream is a common precaution.

Sizing an off-grid system? Call OffGrid Horizon at (302) 496-3554 — we are a family-owned shop and glad to help you match the APEX to a battery bank and load list.

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