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Fortress eFlex 5.4 5.374kWh 51.2V Lithium Ferro Phosphate (LFP) Battery – 105Ah, Parallel up to 15 Units – eFlex 5.4

Fortress eFlex 5.4 5.374kWh 51.2V Lithium Ferro Phosphate (LFP) Battery – 105Ah, Parallel up to 15 Units – eFlex 5.4

Fortress eFlex 5.4 5.374kWh 51.2V Lithium Ferro Phosphate Battery

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SKU PES-ESS-BTS-0281

Fortress eFlex 5.4 5.374kWh 51.2V Lithium Ferro Phosphate (LFP) Battery – 105Ah, Parallel up to 15 Units – eFlex 5.4

OEM Authorized Dealer BABA Compliant Full OEM Warranty 7-10 Business Day Delivery

$1,924.00 USD

$ $1,924.00 USD

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In Stock

Get yours today!

9+ sold

In the last 7 days

Flat Rate Shipping - Calculated at Checkout

Delivery timeframe shown above at checkout

Lifetime Customer Support

Unlimited lifetime support, always available.

In High Demand! Order Now To Secure Your Items

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Specifications

Datasheet

Capacity Kwh 5.374

Capacity Ah 105

Voltage 51.2V

Chemistry LFP (Lithium Iron Phosphate)

Depth Of Discharge Up to 100%

Cycle Life 8000 @ 80% DoD

What is your return policy?

Returns are free in the first 30 days with no restocking or processing fees, although the customer may be responsible for paying return shipping. See our complete return policy on our Shipping, Delivery, and Returns page linked in the footer of this website.

What’s covered by your return policy?

Our returns policy covers all purchases made through Portlandia Electric Supply. For warranty issues, as authorized distributors, we honor the full manufacturer warranty of ALL the brands on our website. See our complete returns and warranty policies on our Shipping, Deliver, and Returns page.

How long will it take to receive my order?

All orders are processed within 72 hours and you can expect delivery on most orders within 5-7 business days. You will receive access to our customer portal after ordering, where it is easy to track all your shipments. See our Shipping, Delivery and Returns page for more details.

What are your financing and payment options?

We offer several ways to pay to make getting your solar kit simple:

Credit Card: if the purchase is greater than your card’s limit, you can split the cost onto multiple cards as well as Paypal, financing through Affirm, and ACH/bank transfer

You can arrange financing during the checkout process, or scroll further down this page for more details. Please note, if you'd like to finance your order, you can do so instantly, right at checkout.

How does your Lifetime Customer Support work?

Our legendary lifetime customer support has helped make us the #1 online solar retailer! We have a dedicated team of solar professionals standing by to help you navigate the world of solar with ease. From selecting the perfect solar kit to installation and beyond, we provide support and expertise at every step of the journey.If you need help with ordering, shipping, troubleshooting, expanding your system, warranty issues, or anything else you have questions about for as long as you own your Portlandia Electric Supply equipment, we’ve got you covered: we’re always only a phone call or email away.

Fortress eFlex 5.4 5.374kWh 51.2V Lithium Ferro Phosphate (LFP) Battery – 105Ah

The Fortress eFlex 5.4 Battery is a state-of-the-art 5.374kWh Lithium Ferro Phosphate (LiFePO₄) energy storage solution designed for residential, commercial, and off-grid solar systems. Known for its reliability, high efficiency, and safety, the eFlex 5.4 by Fortress Power ensures seamless power backup and long-term performance in both standalone and hybrid energy setups.

Product Features

Advanced LiFePO₄ Chemistry

Built with Lithium Ferro Phosphate (LFP) technology, the eFlex 5.4 offers enhanced thermal stability, superior safety, and an extended lifecycle exceeding 6,000 charge/discharge cycles.

Compact & Modular Design

Each 5.374kWh module is stackable and parallel-expandable up to 15 units, providing a scalable energy storage capacity of over 80kWh for larger power requirements.

Smart Battery Management System (BMS)

The integrated BMS ensures real-time monitoring and protection against overcharge, over-discharge, overcurrent, and temperature fluctuations, maximising both safety and efficiency.

Flexible Installation Options

Designed for wall-mount, floor-mount, or rack-mount configurations, making it ideal for various indoor and outdoor applications.

Seamless Inverter Compatibility

Certified to work with leading inverter brands such as Sol-Ark, Schneider, OutBack, Victron, and Growatt for plug-and-play integration.

How It Works

The Fortress eFlex 5.4 stores DC power generated by solar panels or the grid and converts it to usable AC power through a hybrid inverter. Its built-in BMS and communication interfaces (CAN/RS485) ensure synchronised control and optimal energy dispatch between connected batteries and inverters.

Specifications

Model	eFlex 5.4
Battery Type	Lithium Ferro Phosphate (LiFePO₄)
Nominal Energy	5.374 kWh
Nominal Voltage	51.2 V DC
Nominal Capacity	105 Ah
Usable Energy	≈ 5.1 kWh (95% DoD)
Round Trip Efficiency	> 98%
Cycle Life	≥ 6,000 cycles @ 80% DoD
Continuous Discharge Current	100 A
Peak Discharge Current (5s)	200 A
Parallel Capability	Up to 15 units (≈ 80.6 kWh)
Communication Interface	CAN / RS485
Enclosure Rating	IP65 (Indoor/Outdoor Rated)
Operating Temperature	–4°F to 131°F (–20°C to 55°C)
Cooling Method	Natural Convection
Certifications	UL 1973, UL 9540A, UN38.3, UL 9540
Warranty	10 Years (Manufacturer Limited)
Manufacturer	Fortress Power

Specifications verified from official Fortress Power Datasheet, Installation Manual, and Warranty Guide.

What is your return policy?

What’s covered by your return policy?

How long will it take to receive my order?

What are your financing and payment options?

We offer several ways to pay to make getting your solar kit simple:

Credit Card: if the purchase is greater than your card’s limit, you can split the cost onto multiple cards as well as Paypal, financing through Affirm, and ACH/bank transfer

You can arrange financing during the checkout process, or scroll further down this page for more details. Please note, if you'd like to finance your order, you can do so instantly, right at checkout.

How does your Lifetime Customer Support work?

Fortress eFlex 5.4 5.374kWh 51.2V Lithium Ferro Phosphate (LFP) Battery – 105Ah

Product Features

Advanced LiFePO₄ Chemistry

Built with Lithium Ferro Phosphate (LFP) technology, the eFlex 5.4 offers enhanced thermal stability, superior safety, and an extended lifecycle exceeding 6,000 charge/discharge cycles.

Compact & Modular Design

Each 5.374kWh module is stackable and parallel-expandable up to 15 units, providing a scalable energy storage capacity of over 80kWh for larger power requirements.

Smart Battery Management System (BMS)

The integrated BMS ensures real-time monitoring and protection against overcharge, over-discharge, overcurrent, and temperature fluctuations, maximising both safety and efficiency.

Flexible Installation Options

Designed for wall-mount, floor-mount, or rack-mount configurations, making it ideal for various indoor and outdoor applications.

Seamless Inverter Compatibility

Certified to work with leading inverter brands such as Sol-Ark, Schneider, OutBack, Victron, and Growatt for plug-and-play integration.

How It Works

Specifications

Model	eFlex 5.4
Battery Type	Lithium Ferro Phosphate (LiFePO₄)
Nominal Energy	5.374 kWh
Nominal Voltage	51.2 V DC
Nominal Capacity	105 Ah
Usable Energy	≈ 5.1 kWh (95% DoD)
Round Trip Efficiency	> 98%
Cycle Life	≥ 6,000 cycles @ 80% DoD
Continuous Discharge Current	100 A
Peak Discharge Current (5s)	200 A
Parallel Capability	Up to 15 units (≈ 80.6 kWh)
Communication Interface	CAN / RS485
Enclosure Rating	IP65 (Indoor/Outdoor Rated)
Operating Temperature	–4°F to 131°F (–20°C to 55°C)
Cooling Method	Natural Convection
Certifications	UL 1973, UL 9540A, UN38.3, UL 9540
Warranty	10 Years (Manufacturer Limited)
Manufacturer	Fortress Power

Specifications verified from official Fortress Power Datasheet, Installation Manual, and Warranty Guide.

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Customer Success Stories

Troy P

EG4 off-grid base kit, Happy with my purchase.

This is the first stage of my three planned purches. I got the eg4 inverter 6000 XP base kit with six 400 watt panels and the two server rack batteries. Did a little online research and followed the instructions and it got set up without any issues. Right now I'm just running it in my garage on a single outlet and have been running dual 750 watt water distillers with it. Once I get the second inverter and a bunch more panels and batteries, I plan on attaching it to my subpanel in my house that has my lights and outlets and appliances on it. Then I'll get a soft start for my AC and blower and run it on my main panel.

Jacob B

Easy Process, Genuine Support

Trying to pick the correct solar system for your needs can be very technical and frustrating. I wanted to thank Yvhan and the Portlandia Electric supply team for their patience and helpful attitudes through multiple calls. I feel like we were able to narrow it down to what worked for me and my family. My system works great and I couldn't be happier to have picked Portlandia Electric Supply.

Patrick B

Off Grid Solar Purchase

I wanted to get an offgrid solar system for years but didn’t know where to start. I found Portlandia Electric Supply on Facebook and decided to submit a quote. Within 24 hours I had a custom proposal that was almost half the price of the companies I had previously got quotes from. My wife and I decided to order online and the kit came in a timely manner and it was an easy install. Great company to work with!

James Martin

Highly Recommend

I would like to take the time to express the outstanding service that I was provided with by Portlandia Electric Supply. They provided me with all the answers to my questions, and after reviewing our quote over the phone I felt comfortable proceeding to order my kit. It’s exactly what I needed and they were there to help us over the phone when we had questions installing it. I highly recommend others in need to choose Portlandia Electric Supply.

Brian H

Solar Kit for Mobile Work Van

As a professional videographer, I needed reliable power on the go.Portlandia Electric Supply Delta Pro and roof-mounted panels were the perfect solution. Setup was easy, and the kit included everything needed. The Delta Pro powers my cameras, lights, laptop, and a small fridge with impressive battery capacity.

Keith S

Best Tech Support

You folks have been wonderful guiding me through the ins and outs of going solar. Plus your tech guys Rod and Nelson are the absolute best. They explained all the different aspects of inverters, batteries and how to keep them in top condition. Too much more to put here… but no other company has the 100% tech support you provide for your customers!

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Great Experience

My experience with Portlandia Electric Supply has been excellent. Before the sales, they answered all my questions to assure that I got what I needed. After the sales they continued to support me with answers and help. I had a warranty issue with a unit, and it was handled as well as possible. I would recommend them to anyone looking to go solar.

Troy P

EG4 off-grid base kit, Happy with my purchase.

Jacob B

Easy Process, Genuine Support

Patrick B

Off Grid Solar Purchase

James Martin

Highly Recommend

Brian H

Solar Kit for Mobile Work Van

Keith S

Best Tech Support

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