Fortress Power Lithium Iron Phosphate Battery EFlex 5.4 KWh

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 lightweight unit can be wall mounted. The eFlex also comes with racks that can be used to stack multiple units on the floor. It is designed to fit into standard 24-inch computer racks.


The eFlex battery is scalable up to 200 kWh per inverter via CAN communication cables, to support Residential, Commercial and Industrial Storage Projects. The unit uses safe and high energy density prismatic Lithium-Iron-Phosphate cells. The 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. It has the highest round trip efficiency in the industry at 98%. This unit has wall mounting functionality and fits well into standard server racks for large systems.


  • 98% Roundtrip efficiency
  • High Durability and Long-Lasting
  • Safe Lithium Iron Phosphate Technology (LiFeP04)
  • Remote Monitoring
  • Cell level Monitoring and Balancing
  • Close-loop communication with many hybrid inverters
  • 10 year warranty with the safe and premium prismatic Lithium-Iron-Phosphate cells
  • High energy throughput the exceptional life span (6000+ cycles) and high round-trip efficiency (>98%)
  • Expandable from 5.5kWh to 81 kWh for small and large facilities
  • The compact and easy-to-install unit can be wall mounted or floor-standing. It also fits well into standard server racks for large systems.
  • The battery has a built-in data storage Wi-Fi for remote monitoring and troubleshooting ability.

The eFlex 5.4 is now UL 9540 listed. UL 9540 is the latest UL safety standard for energy storage systems (ESS) and equipment. It addresses the safety of ESS intended to store energy from grid, renewable, or other power sources and provide electrical or other types of energy to loads or power conversion equipment. The standard’s goal is to ensure that electrical, electro-chemical, mechanical, and thermal ESS operate at an optimal level of safety for both residential and industrial energy users.

Additional information

Weight 108 lbs
Dimensions 18 × 23 × 7.3 in

Fortress Power


eFLEX 5.4

Rated Power Output [W]


Warranty [Years]




Fortress Power is a leading provider of energy storage solutions for solar consumers. Their products, including the Fortress Power eFlex and Fortress Power eVault, are designed to provide reliable and cost-effective energy storage for homes and businesses. The eFlex is a modular battery system that can be expanded as needed to meet changing energy demands, while the eVault is a high-capacity battery designed for longer-term energy storage. Both products offer features such as remote monitoring and easy installation. Fortress Power's commitment to quality and sustainability, as well as their focus on customer service and support, make them a trusted choice for solar energy consumers in need of energy storage solutions.