Product Description

This kit pairs the EG4 FlexBOSS18 hybrid inverter — up to 18 kW of PV input and 13 kW of continuous split-phase AC output per EG4 — with the EG4 WallMount 314Ah Indoor battery, a self-heating 16 kWh unit built for garages, basements, and utility rooms. Per EG4, this battery-and-inverter pairing carries the UL9540 energy storage system designation. Configure one to three batteries for 16, 32, or 48 kWh. OffGrid Horizon is a family-owned authorized EG4 dealer, and every kit ships with full manufacturer warranty support.

Who This Is For

Homeowners installing storage indoors — a garage wall, a basement utility corner — who want a matched single-brand system with the permitting documentation many building departments ask for. Per EG4, the WallMount Indoor forms a UL9540 system with the FlexBOSS18, and its self-heating cells keep charging available when an unheated garage drops below freezing. If your loads are typical residential, the FlexBOSS18's 13 kW output covers most homes.

Key Features

  • UL9540 system designation with the FlexBOSS18, plus UL1973 certification and UL9540A test data on the battery — exactly as EG4 publishes
  • Self-heating batteries — a 448W internal heater activates at or below 32°F per EG4, so winter does not stop charging in unheated spaces
  • Up to 18 kW of PV input (600VDC max, up to 4 strings per EG4) with 13 kW continuous split-phase 120/240V output
  • 10 kW continuous output from battery alone per EG4 — the figure that matters at night and during outages
  • 16 kWh per battery, 10,000-cycle rating at 80% depth of discharge per EG4
  • Closed-loop communication over CAN/RS485 with app-based remote monitoring
  • 293.2 lb per battery — the lightest 16 kWh unit in the WallMount line, wall- or floor-mounted

Why EG4

EG4 Electronics is a Texas-based manufacturer that builds both halves of this system, publishes full spec sheets and fire-safety test data, and backs the inverter and batteries with 10-year warranties. Because one company engineers the pairing, the UL9540 system documentation covers the exact hardware in this kit.

What's In the Kit

  • 1 x EG4 FlexBOSS18 hybrid inverter — split-phase 120/240V, UL3141 and UL1741 certified per EG4
  • 1, 2, or 3 x EG4 WallMount 314Ah Indoor batteries (16 kWh each) — the listed configuration includes one battery; select your capacity from the product options

Solar panels, racking, and array wiring are site-specific and sold separately. The system also operates as battery backup without solar.

Specifications

Inverter EG4 FlexBOSS18 hybrid, split-phase 120/240V
PV input Up to 18 kW (STC), 600VDC max, up to 4 strings, per EG4
AC output 13 kW continuous (grid-tied with solar contribution); 10 kW from battery alone, per EG4
Inverter certifications UL3141; UL1741, per EG4
Battery EG4 WallMount 314Ah Indoor, 51.2V, 16 kWh nominal per unit
Capacity options 16 / 32 / 48 kWh (1, 2, or 3 batteries)
Battery output 200A max continuous discharge per unit, per EG4
Battery enclosure IP20 — indoor installation
Battery certifications UL1973; UL9540A; UL9540 with FlexBOSS18, per EG4
Self-heating 448W heater, on at 32°F or below, per EG4
Battery cycle life 10,000 cycles at 80% DoD, per EG4
Battery dimensions / weight 34.1 x 18.1 x 9.6 in / 293.2 lb per unit
Communication Closed-loop CAN/RS485; app-based remote monitoring
Warranty Inverter 10 years; batteries 10 years or 10,000 cycles, per EG4
Base SKU K0216

Grid-Tied, Backup, or Off-Grid

Grid-tied: the FlexBOSS18 manages solar production, battery charging, and export under UL1741 interconnection rules — your utility and AHJ govern export permissions. Backup: when the grid drops, the system transfers to battery power; one battery (16 kWh) carries essential circuits overnight, while 32 or 48 kWh supports whole-home coverage or multi-day outages. Off-grid: the same hardware runs fully off-grid, sized by your daily load and sun hours. For whole-home microgrid control — AC coupling, smart load management, and generator integration per EG4 — add the EG4 GridBoss 200A MID.

Inverter Compatibility

The batteries in this kit run closed-loop with the included EG4 FlexBOSS18 hybrid inverter, so state-of-charge and charge parameters stay coordinated out of the box — and per EG4 the pairing carries the UL9540 system designation. Individual WallMount 314Ah Indoor batteries are available separately when you are ready to expand.

Installation

Installation must be performed by a licensed electrician — the inverter interconnects with your main panel and, in grid-tied modes, with the utility, and energy storage installations require local permits and inspection. Each battery weighs 293.2 lb and mounts to the wall or floor per EG4's manual; anchor wall-mounted units into structural framing and plan for lifting equipment. The batteries are IP20 rated and must be installed indoors; the NEMA 4X inverter can mount outside nearby if preferred. Follow EG4's installation manuals for clearances and torque values, and confirm indoor energy-storage placement rules with your building department.

Warranty & Support

Per EG4, the FlexBOSS18 carries a 10-year warranty and each WallMount Indoor battery is covered for 10 years or 10,000 cycles, whichever comes first. Register your equipment with EG4 after purchase and keep your OffGrid Horizon invoice — as an authorized dealer, our records document your coverage. For warranty or configuration help, call us at (302) 496-3554.

Shipping

Kits ship by LTL freight on pallets within the United States, curbside with a liftgate. Count every piece against the packing list and inspect for damage before signing the delivery receipt — note any issues with the driver to preserve your freight claim.

Frequently Asked Questions

How many batteries are included?

The base configuration includes one 16 kWh battery. Select the 2-battery (32 kWh) or 3-battery (48 kWh) option from the product configuration menu before checkout.

What does the UL9540 system designation mean for permitting?

UL1973 covers the battery, UL9540A is a fire-safety test method, and UL9540 covers the complete energy storage system. Per EG4, this battery achieves UL9540 when paired with the FlexBOSS18 — documentation many building departments request for indoor installations.

Why do indoor batteries need self-heating?

LiFePO4 cells cannot accept charge below 32°F, and detached garages and unheated basements routinely drop below freezing. Per EG4, the heater switches on at 32°F and off at 37°F, keeping charging available all winter.

Can I add batteries later?

Yes — per EG4 the WallMount 314Ah Indoor parallels up to 32 units. Most owners start with one or two and expand.

Are solar panels included?

No. Panels, racking, and array wiring are sized to your site and sold separately. The kit operates as grid-charged battery backup without any solar attached.

Should I pick the Indoor or All-Weather kit?

Indoor (this kit) when batteries live in a garage, basement, or utility room — lighter units plus the published UL9540 pairing. All-Weather when batteries must mount outside in an IP67 enclosure.

Not sure what your inspector will want to see, or how many batteries your loads need? Call OffGrid Horizon at (302) 496-3554 — our family-owned team helps with both before you order.

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