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Fortress Power
Genuine Fortress Power gear with the full manufacturer warranty, shipped free to the lower 48.
This Fortress Power category page lists the eFlex Max, a 5.4kWh 48V LFP battery, from $1,789. Only one model is in stock, so it is easy to evaluate against other 48V storage options. It fits residential solar-plus-storage systems that run at 48V, where lithium iron phosphate chemistry offers long cycle life. Before ordering, confirm your inverter supports this battery and think about how many units you need for the loads you want to cover. Free shipping to the contiguous US applies, and we are happy to answer pairing questions.
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ECO100 $100 off $1,500+
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Fortress Power offers advanced lithium-based energy storage systems designed to meet residential, commercial, and off-grid needs. Known for their safety, efficiency, and seamless integration with solar technology, Fortress Power products support energy independence and long-term savings. Whether you're building a resilient backup system or optimizing solar performance, Fortress Power delivers scalable and smart energy solutions backed by American engineering and technical support.
The Fortress Power Batteries collection features some of the most advanced and trusted lithium energy storage solutions available today. Built with safety, reliability, and long-term performance in mind, both the Fortress eVault and eFlex batteries are engineered for homeowners, solar installers, and commercial users who need dependable, scalable energy storage for grid-tied, off-grid, or hybrid solar systems.
Fortress Power batteries use LiFePO₄ (Lithium Iron Phosphate) chemistry, known for its high thermal stability, long cycle life, and safe operation, making them ideal for residential energy independence, backup power, and peak shaving applications.
The Fortress Power eVault is a high-capacity battery designed to deliver reliable energy for full-home backup or large-scale energy storage systems. With up to 18.5kWh of usable capacity per unit, it’s perfect for homes with high energy consumption or critical backup needs.
Capacity: 18.5kWh usable
Battery Chemistry: LiFePO₄ (safe and stable)
Cycle Life: 6,000+ cycles at 80% depth of discharge
Voltage: 48V nominal
Scalability: Stack multiple eVaults for larger systems
Communication: CAN/RS485 compatible with Sol-Ark, Schneider, Victron, and more
Warranty: 10 years
Use Cases: Whole-home backup, time-of-use offset, solar self-consumption
With its large capacity and integration-ready design, the eVault is ideal for homes running on hybrid inverters or using solar to reduce dependency on the grid.
The Fortress Power eFlex battery offers the same proven LiFePO₄ technology in a smaller, more flexible format. It provides 5.4kWh of storage per unit and is designed for wall-mounted, floor-mounted, or rack-mounted installation - perfect for tight spaces, small homes, or modular battery banks.
Capacity: 5.4kWh usable per battery
Battery Chemistry: LiFePO₄
Cycle Life: 6,000+ cycles
Voltage: 48V
Stackable: Link multiple units for systems up to 81kWh+
Mounting Options: Wall, rack, or floor
Inverter Compatibility: Works with Sol-Ark, Victron, Schneider, and more
Warranty: 10 years
Use Cases: Modular backup systems, RVs, small homes, commercial racks
The eFlex is a top choice for installers who need space-saving, customizable storage that can grow with the user’s energy needs.
U.S.-based company with strong support network
Field-proven LiFePO₄ chemistry for safety and reliability
Seamless inverter compatibility with top hybrid brands
Advanced Battery Management System (BMS) built-in
10-year warranty and long service life
Flexible installation options for residential and commercial setups
Whether you’re powering an entire home during outages or maximizing your solar investment, Fortress Power batteries deliver the performance and peace of mind professionals trust.
Residential solar energy storage
Whole-home or partial backup
Time-of-use optimization
Commercial solar applications
Remote properties and off-grid living
With Fortress Power eVault and eFlex, you get premium lithium storage solutions that scale to your lifestyle, installation, and power requirements. Discover the Fortress Power advantage today and bring resilience, efficiency, and independence to your energy system.
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