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BigBattery

BigBattery ETHOS + EG4 FlexBOSS18 Kit | 10.24–30.72 kWh | Split-Phase Home ESS

SKU K0230

Regular price: $6,055.00

Regular price: $6,055.00

✅ Order by 12:00 PM EST and processing starts the same day (ships within 1–2 business days). Free, insured US shipping — delivery in 4–7 business days. Oversized items ship via LTL freight and we coordinate delivery with you by phone.

Product variants

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OffGrid Horizon Family Owned and Operated

🏔️ OffGrid Horizon is family-owned & off-grid obsessed. Read our story →

Shipping: how fast & how it works

Free standard shipping on every US order — no shipping charges at checkout, no hidden fees, and every shipment is insured against loss or damage.

Processing: 1–2 business days. Order before 12:00 PM EST and processing begins the same day.
Delivery: 4–7 business days via USPS, UPS or FedEx. Tracking is emailed the moment your order ships.
Large items (solar kits, batteries, shelters): delivered by LTL freight carriers such as FedEx Freight, Old Dominion or XPO. The carrier calls ahead to schedule a delivery window — please inspect the pallet and note any damage on the delivery receipt before signing, and we’ll take care of the rest.

Questions about delivery to your location? Call (302) 496-3554 (Mon–Fri, 9am–4pm EST) — we’re happy to check before you order.

What is your Return Policy?

At OffGrid Horizon, we want every customer to shop with confidence. If something doesn’t go as planned, we’ve made returns and refunds simple and fair. Here’s how it works:

1. Return Window

You can request a return within 30 days of receiving your order. Unfortunately, we’re unable to accept returns after that time frame.

2. Who Pays for Return Shipping?

If your item arrives damaged, defective, or incorrect, we’ll cover the return shipping cost — and you’ll receive a full 100% refund or replacement, including any original shipping costs.
If you’re returning an item because you changed your mind, you’ll be responsible for return shipping, and a 25% restocking fee applies.

3. Damaged or Defective Items

Received something broken or not working properly? Contact us within 30 days. We’ll provide a prepaid return label and once the item is returned and inspected, we’ll issue either a full refund or a replacement.

4. Changed Your Mind?

If you no longer want the item, you can return it within 30 days — as long as it’s unused, unopened, in its original packaging, and in resellable condition.

5. Refund Processing

Once we receive and approve your return, we’ll send a confirmation email and issue a refund to your original payment method within 7 business days. Please allow additional time for banks or credit card companies to process and reflect the refund.

How to start a return: email sales@offgridhorizon.com or call (302) 496-3554 (Mon–Fri, 9am–4pm EST) with your order number — we’ll send return instructions and your RMA right away.

Product Description

This kit pairs BigBattery's stackable ETHOS 48V LiFePO4 battery platform with the EG4 FlexBOSS18 hybrid inverter. Per EG4, the FlexBOSS18 delivers 13 kW of continuous output (10 kW on battery alone) with up to 18 kW of solar input utilization; per BigBattery's FlexBOSS18 listing it is a split-phase, 3-MPPT unit with remote Wi-Fi monitoring. ETHOS storage in this listing is configurable from 10.24 to 30.72 kWh, and per BigBattery the battery and inverter operate with closed-loop communication.

Who This System Is For

Homeowners building a grid-interactive storage system around the newer FlexBOSS ecosystem — solar self-consumption, time-of-use offset, and outage backup — with more output headroom than the 18kPV's 12 kW and a direct path to GridBOSS whole-home management. The stackable ETHOS tower suits buyers who want to start with essential-circuit storage and add 5.12 kWh modules as needs grow.

Key Features

13 kW continuous output with PV contribution and 10 kW battery-only output, per EG4
Up to 18 kW of solar input utilization, per EG4, across 3 MPPTs per BigBattery's FlexBOSS18 listing
Split-phase 120/240V output feeds standard North American panels, per BigBattery's listing
UL 3141 and UL 1741 listed inverter, per EG4; ETHOS battery carries UL9540, UL9540A, UL1973, and UN38.3, per BigBattery
Closed-loop communication between ETHOS and compatible EG4 inverters, per BigBattery
Remote Wi-Fi monitoring, per BigBattery's FlexBOSS18 listing
Expandable: stack additional ETHOS modules — up to 16 parallel connections per control box, per BigBattery

Why BigBattery

BigBattery is a US-based energy storage company that has been building lithium battery systems since 2011 and, per BigBattery, is trusted by more than 50,000 Americans. BigBattery states its products are designed and engineered in Texas, includes free lifetime tech support with every product, and backs its batteries with a 12-Year Limited Warranty — described by BigBattery as "the longest warranty in the battery industry." OffGrid Horizon is a family-owned authorized BigBattery partner.

What's In the Kit

1 × EG4 FlexBOSS18 hybrid solar inverter
BigBattery ETHOS 48V 5.12 kWh LiFePO4 modules — capacity for this listing is configurable from 10.24 to 30.72 kWh (2–6 modules)

Please call (302) 496-3554 to confirm the module count and configuration that ships at the listed price. BigBattery lists ETHOS inverter connectors and battery-to-battery connectors as separate accessories, so also confirm cabling with your order. Solar panels, racking, and array wiring are sold separately. For whole-home load management, AC coupling, and generator support, ask about the EG4 GridBOSS MID.

Specifications

Battery	BigBattery ETHOS, stackable LiFePO4 — see the ETHOS battery system
Module capacity	5.12 kWh / 100Ah per module, 51.2V nominal
Capacity (this listing)	Configurable 10.24–30.72 kWh — call to confirm configuration
Max continuous discharge	200A (2-module stack) / 250A (3+ modules), per BigBattery
Battery communications	CAN bus / RS485; closed-loop with EG4, per BigBattery
Battery certifications	UL9540, UL9540A, UL1973, UN38.3, per BigBattery
Cycle life	3,500–5,000 cycles (80% DoD, 0.5C), per BigBattery's spec sheet
Battery warranty	BigBattery 12-Year Limited Warranty
Inverter	EG4 FlexBOSS18 hybrid (model IV-13000-HYB-AW, per EG4)
AC output	13 kW continuous with PV; 10 kW battery-only, per EG4; split-phase 120/240V
PV input	Up to 18 kW solar input utilization, per EG4; 3 MPPTs per BigBattery's listing
Operating modes	Grid-tied, off-grid, battery backup (grid export subject to utility approval)
Monitoring	Remote Wi-Fi monitoring, per BigBattery's listing
Inverter certifications	UL 3141, UL 1741, per EG4
Inverter warranty	10-year, per EG4 (registration required — see below)

Grid-Tied, Off-Grid, or Backup?

The FlexBOSS18 is a hybrid inverter: per BigBattery, ETHOS + FlexBOSS configurations are grid-tied UL9540 systems, and per EG4 the unit is UL 3141 / UL 1741 listed for grid interconnection. It supports solar self-consumption, backup during outages, and off-grid operation. Grid export requires an approved interconnection agreement with your utility. Whole-home backup is achievable with proper design and load management — coverage is load-dependent, and heavy simultaneous 240V loads should be reviewed against the 10 kW battery-only output figure for nighttime outages.

Installation

All AC and DC wiring — panel interconnection, grounding, bonding, and overcurrent protection — must be performed by a licensed electrician in accordance with the National Electrical Code (NEC) and local amendments. Residential energy storage installations typically require a permit and inspection, and grid-tied operation requires an approved interconnection agreement with your utility before the system may export power. Your installer should verify conductor sizing, disconnects, and clearances against current NEC requirements for energy storage systems.

Warranty & Support

Battery — BigBattery 12-Year Limited Warranty. Per BigBattery: "If any covered component within your battery fails due to a defect in materials or workmanship within the 12-year warranty period, we will repair or replace the battery at our cost." Included accessories carry a 1-year warranty per BigBattery, and BigBattery provides free lifetime tech support for all its products.

Inverter — EG4 10-year warranty. Per EG4, the FlexBOSS18 carries a "10-year Full Parts Replacement or Full Product Replacement Warranty from the date of original inverter purchase," and the warranty must be registered within the first year of purchase (or proof of purchase from an EG4 authorized distributor provided) to remain valid.

Returns and warranty claims require an RMA. Contact us before shipping anything back — all returns must be authorized with a Return Merchandise Authorization first. OffGrid Horizon is a family-owned authorized BigBattery partner: call (302) 496-3554 and we will help open the claim and coordinate service.

Shipping

This kit ships as palletized LTL freight within the continental United States; curbside liftgate delivery is standard for residential addresses. ETHOS towers are heavy — 273 lb for a two-module stack per BigBattery — so plan for help on delivery day. Before signing the delivery receipt, count the pieces and inspect the packaging; note any damage or shortage on the receipt with the driver and contact us immediately so we can open a freight claim. Per BigBattery, standard domestic orders are projected to take 7–12 days to deliver.

Frequently Asked Questions

What exactly ships at the listed price?

This listing covers the EG4 FlexBOSS18 inverter plus ETHOS battery storage configurable from 10.24 to 30.72 kWh. Call (302) 496-3554 before ordering and we will confirm the module count, included accessories, and configuration options for this SKU.

How is the FlexBOSS18 different from the 18kPV?

Both accept up to 18 kW of PV, per EG4. The FlexBOSS18 offers 13 kW continuous output with PV (versus 12 kW), carries the newer UL 3141 listing, and is designed around the GridBOSS ecosystem for whole-home load management and AC coupling.

FlexBOSS18 or FlexBOSS21?

Per EG4, the FlexBOSS21 steps up to 21 kW of usable PV input and up to 16 kW of AC output with solar contribution. If your array or simultaneous loads are larger, consider the FlexBOSS21 kit; otherwise the FlexBOSS18 covers most homes.

Will this back up my whole home?

Coverage is load-dependent. 13 kW continuous output (10 kW battery-only at night, per EG4) carries most household circuits; heavy simultaneous 240V loads should be reviewed during design, and GridBOSS smart-load control can help manage them.

Can I add more battery later?

Yes — ETHOS stacks in 5.12 kWh steps, with up to 16 parallel connections per control box per BigBattery, so capacity can grow without replacing the inverter.

Does it work without solar panels?

Yes. The system operates as grid-charged battery backup, and you can add panels later — up to 18 kW of solar input utilization, per EG4.

Want help choosing between FlexBOSS models or sizing your battery? Call OffGrid Horizon at (302) 496-3554 — family-owned, authorized BigBattery partner.