Fortress Power eFlex 5.4 – LFP Battery

The Fortress Power eFlex 5.4 kWh is a scalable energy storage battery solution with high efficiency, high durability, and using the safest battery technology! This Lithium Iron Phosphate battery features user-friendly integrations including remote monitoring, cell-level monitoring, and close-loop communications with many hybrid inverters. 

Wall bracket included






Fortress Power eFlex – 5.4 kwh Lithium Iron Phosphate Battery

Fortress Power announces the eFlex 5.4 kWh scalable energy storage battery solution!

This unit uses safe and high energy density prismatic Lithium Iron Phosphate cells.

The eFlex 5.4 kwh battery has a built-in data storage and Wi-Fi for remote monitoring and troubleshooting ability. The smart relay-based Battery Management System (BMS) supports closed-loop communication with various 48V hybrid inverters on the market. Additionally, the BMS monitors and balances the voltage and temperature of each individual cell to maximize reliability and longevity.

The Fortress Power eFlex has the highest round trip efficiency in the industry at 98%! Additional features include wall mounting hardware, and it fits well into standard server racks for large systems.


fortress eflex 5.4

Fortress Power eFlex 5.4
Total Energy 5.4 kWh
Max Charge Current (continuous) 55 A
Max Discharge Current (continuous) 68 A
Max Pulse Current (for 5 sec) 130 A
Capacity 105 Ah
Voltage Range 44 – 58.4 V
Charging Temperature 32 – 113ºF
Discharging Temperature 32 – 140ºF
Storage Temperature 32 – 95ºF
Dimensions (HxWxD) 18″ x 23″ x 7.3″
Weight 108 lb
Life Cycles 6,000 @ 80% DoD
Round Trip Efficiency >98%


Why The Fortress Power eFlex Is Dominating the Market

High Durability & Long Lasting

10 Year Warranty with the safe and premium prismatic Lithium-Iron-Phosphate cells. 

Lowest Cost Per Cycle

High energy throughput with exceptional life span (6000+ cycles) and high round-trip efficiency (>98%). Thanks to the exceptional life span of an LFP battery, you will connect to the lowest energy costs available!


Fortress eFlex 5.4 Lithium Iron Phosphate (LFP; LifePO4) battery can be easily integrated into a new or existing PV system to support back-up, Off-Grid, Self-supply, Time-of-Use or Demand Curtailment applications.


The new eFlex battery is scalable up to 200 kWh per inverter via CAN communication cables, to support Residential, Commercial and Industrial Storage Projects.

Flexible Installation

The compact and easy-to-install unit can be wall mounted or floor-standing.The eFlex also comes with racks that can be used to stack multiple units on the floor. It is brilliantly designed to fit into standard 24-inch computer racks!

Remote Monitoring

The battery has a built-in data storage Wi-Fi for remote monitoring and troubleshooting ability


More Outstanding Features


Waterproof and Saltwater Resistant Aluminum Enclosure

The eFlex 5.4 comes with a light-weight Aluminum case, which is a popular choice for preventing salt-water corrosion, among various metal enclosures. Also, the slim-looking cabinet has an IP 65 waterproof rating. However, we still recommend that you place the unit in an indoor environment to obtain the 6000+ charge cycles.

Safe and reliable Prismatic Lithium Iron Phosphate (LFP; LiFePO4) cells

eFlex 5.4 is engineered with the advanced Lithium iron phosphate (LFP) technology, which provides the highest level of safety, thermal-stability, and reliability. We selected Prismatic Cells over Cylindrical and Porch Cells for many good reasons. First, prismatic cells are more efficient and more robust; Second, they have the lowest degradation rate; Third, the prismatic cells have superior thermal stability due to their excellent heat dissipation characteristic.

Sturdy relay-based Battery Management System (BMS) circuit board for fast charging/discharging.

Many other lithium batteries on the market use simple MOSFET based BMS, while eFlex unit uses our proprietary relay-based BMS. The sturdy BMS circuit board not only provides multi-level safety protection, but it also supports fast charging and discharging.

Closed-loop communication with inverters/chargers

Our engineers built the smartness into the BMS. It enables the BMS to report Voltage, Current, State-of-Charge (SoC) and temperature to the inverters/chargers. This closed-loop communication ensures your energy storage system works seamlessly.

Fortress Power Compatibility 

Fortress Lithium Iron Phosphate batteries are designed to work with most 48VDC inverter and chargers available on the market. Below is a list of compatible inverters and chargers.

Brand Inverter/Charger Configuration
Sol-Ark 8 KW & 12 KW Inverter AC or DC coupled
Schneider Conext XW MPPT charge controller; Conext XW+/XW pro series AC or DC coupled
Outback Skybox, FLEX max charge controller (48V), FLEXpower series (48V); Radian series (48V); FXR(A) and FXR (E) series (48V); GVFX and GVFX series (48V); AC or DC coupled
Magnum MS 4448PAE; MS 4048-20B AC or DC coupled
SMA SUNNY ISLAND 4548-US/6048-US; SUNNY ISLAND 3.0M/4.4M/6.0H/8.0H AC coupled
Victron Phoenix VE.Direct Inverter; MultiPlus and Quatro Inverter/Charger; Skylla-TG Charger; General; Color Control or Venus GX DC coupled
Morning Star TriStar MPPT 600V; TriStar MPPT; Tristar PWM DC coupled
Midnite Solar Solar Classic 150, 200 & 250; Solar Classic 150, 200 & 250-SL DC coupled

If you can’t find the inverter you are using on the list, please call us a(864) 915-1855or email us at


Data Sheets & Literature


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