EG4 FlexBOSS18 48V Hybrid All-In-One Inverter, 10kW-13kW AC Output, 18kW Solar Input, 120/240V Split Phase, NEMA 4X, UL 1741 & UL 9540

About the EG4 FlexBOSS18 Hybrid Inverter

The EG4 FlexBOSS18 puts an inverter, two solar charge controllers, a 208A battery charger and a 90A grid pass-through in one wall-mounted box. As a 13kW AC hybrid inverter it runs heavy household loads on a single unit while the sun is up, then holds 10kW from the battery after dark. Set it to sell solar back to the grid, shave peaks off your utility bill, hold zero export, or run fully off-grid, all from the EG4 app or Monitor Center.

At under 50 dB from 3 ft away, it is quiet enough for a garage or utility room wall, and the NEMA 4X enclosure lets it live outdoors too. Idle draw stays under 60W, so more of your battery reaches your loads overnight.

13kW With Solar and 195A LRA for Well Pumps and Central AC

Motor loads are where an inverter earns its keep. The FlexBOSS18 delivers 20kW for half a second, 15kW for a full second and 13.5kW for a minute, backed by 195A of locked rotor current. That is the headroom to start a 5-ton air conditioner, a large well pump or a welder. The pure sine output (under 5% voltage distortion) keeps computers, variable-speed HVAC and other sensitive electronics well served.

Each leg carries 5kW (41.67A) continuously, so spread your big 120V loads across L1 and L2 when you lay out the panel.

18kW of Solar on Two 600V MPPTs

With up to 600Vdc per input, long series strings move their power on smaller wire and skip the combiner box. MPPT 1 takes three string inputs and MPPT 2 takes two, with 26A per tracker (31A short-circuit), so an east array and a west array, or a shaded string, each get their own tracker.

EG4 rates full power from 250 to 440Vdc, with 360Vdc as the sweet spot, and the inverter faults at 550Vdc, so keep cold-weather string voltage under that line. Our team is happy to help with string sizing.

FlexBOSS18 vs 18kPV: 90A Pass-Through or 200A Bypass

The EG4 18kPV is the other hybrid buyers weigh, and the real difference is the grid connection. The 18kPV has a 200A bypass built in, so it can sit between the meter and a whole-home panel on its own. The FlexBOSS18 passes 90A through to its load port, which covers a critical loads panel or an off-grid build, and it pairs with GridBOSS when you want whole-home service.

In exchange, the FlexBOSS18 brings more motor-starting current (195A LRA against 180A) and lower idle draw (under 60W against about 70W). If you need more output, the FlexBOSS21 steps up to 16kW with solar and three MPPTs.

Pair With GridBOSS for Whole-Home Backup and Generator Input

The EG4 GridBOSS turns one or more FlexBOSS18s into a whole-home system. It takes the 200A service entrance connection and adds generator input, four smart load ports and AC coupling with existing or new grid-tie inverters. It also lets you mount the inverters wherever they fit best, away from the main panel.

With GridBOSS in the system, the inverter's load port and included CTs go unused because GridBOSS does the metering. Update each FlexBOSS18 to firmware 1E1E or later before pairing.

Battery Sizing: 300Ah Minimum and UL 9540 WallMount Pairings

EG4 requires at least 300Ah of 48V battery for the FlexBOSS18 to deliver its rated output. A single 280Ah WallMount needs a second battery beside it, while one EG4 WallMount 314Ah Indoor clears the minimum by itself.

The FlexBOSS18 is UL 9540 certified as an energy storage system with the WallMount All Weather 280Ah, WallMount Indoor 280Ah and WallMount 314Ah Indoor, which is the system listing many AHJs (Authorities Having Jurisdiction) look for on permitted installs. Closed-loop CAN and RS485 communication also works with a range of other lithium brands on EG4's compatibility list, and EG4 strongly recommends closed loop for any lithium bank.

Battery Cables and DC Protection

The battery terminals take two cables per pole, four in total, torqued to 230 in-lbs (26 Nm). EG4 sizes them by run length: 1/0 AWG up to 16 ft, 2/0 up to 21 ft, 3/0 up to 26 ft and 4/0 up to 33 ft.

We build our custom battery cables to order in exactly those gauges and cut them to the length your layout needs. The FlexBOSS18 has an integrated 250A battery breaker, and EG4 also calls for a separate DC overcurrent device or disconnect between the battery and the inverter. A Class T fuse handles the fault current a 48V lithium bank can deliver.

Rapid Shutdown and Outdoor Installation

The built-in RSD transmitter and front-panel RSD button cut AC output and bring PV conductors under 30V within 30 seconds, per NEC 690.12. With supported EG4 batteries on closed-loop communication, the same button also triggers the battery disconnect, and an external normally closed E-stop can be wired in if your AHJ asks for one. AFCI and GFDI protection come built in.

The NEMA 4X enclosure handles outdoor and damp locations, and EG4 recommends a spot out of direct sun, rain and snow, such as under an eave. Leave 6 in (150 mm) on each side and 12 in (300 mm) above. It runs from -13°F to 140°F (-25°C to 60°C) with derating above 113°F (45°C), and EG4's altitude derating guide applies above 6,561 ft (2,000 m). At 115 lb, plan on two people for the lift.