What makes the Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP battery different from other lithium batteries?

The Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP battery uses lithium iron phosphate chemistry, which provides higher safety, longer cycle life, and better thermal stability compared to many other lithium battery types.

Is the Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP battery suitable for solar energy storage?

Yes, the Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP battery is ideal for solar systems, as it efficiently stores excess solar energy and delivers consistent power when sunlight is unavailable.

Can multiple Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP batteries be connected together?

Yes, this battery supports parallel connections, allowing users to scale their energy storage capacity based on growing power requirements.

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Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP battery - eFlex Max 5.4

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SKU PES-ESS-BTS-0244

Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP battery - eFlex Max 5.4

$2,884.38 USD

$ $2,884.38 USD

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SKU:PES-ESS-BTS-0244
Documents:
Datasheet
Installation Guide
Warranty
Height: 7.2
Isfollow: true
Isindex: true
Length: 17.5
Mpn number: eFlex Max 5.4 (IP65 rated)
MPN Number: eFlex Max 5.4 (IP65 rated)

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In Stock

Get yours today!

9+ sold

In the last 7 days

Flat Rate Shipping - Calculated at Checkout

Get it between Mon, Sep 22 - Wed, Sep 24

Free Returns

Free Returns within 30 Days of Purchase

Lifetime Customer Support

Unlimited lifetime support, always available.

View full details

Fortress eFlex Max 5.4 kWh battery — rugged 48 V LiFePO₄ (IP65)

The Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP battery is a high-performance lithium energy storage solution designed for homeowners and businesses seeking dependable, long-lasting power. Built with advanced lithium iron phosphate (LFP) technology, this battery offers superior safety, efficiency, and durability for modern energy needs, including solar storage, backup power, and off-grid applications.

With a compact design and robust construction, the battery ensures stable performance even in demanding environments. Whether you are upgrading an existing energy system or building a new one, this battery delivers consistent power output and long cycle life for maximum value.

Fortress eFlex Max 5.4 kWh battery comes with an outdoor-rated aluminum enclosure (IP65), 48 V/105 Ah LFP cells, and closed-loop inverter comms—for reliable performance in harsh climates.

Key features

Fortress eFlex Max 5.4 kWh battery offers high cycle-life (≈8,000 @ 80% DoD), >98% RTE, OTA updates, RS485/CAN, and flexible mounting options.

5.4 kWh energy · 48–55 V operating · 105 Ah capacity
Max charge 100 A · max discharge 60 A (cont.)
Aluminum IP65 case with improved thermal design
Wall/floor/rack mount; compatible with Envy & third-party 48 V inverters

Specifications

**Fortress eFlex Max 5.4 kWh battery** — specification box
Total energy	5.4 kWh
Nominal / operating V	48 V / 48–55 V
Capacity	105 Ah
Charge / discharge (cont.)	100 A / 60 A
Round-trip efficiency	>98%
Enclosure	IP65 aluminum; wall/floor/rack mount
Dimensions (L×W×H)	17.5″ × 24.2″ × 7.2″
Weight	≈108 lb
Temperature (charge / discharge)	32–114 °F / −4–131 °F
Cycle life	~8,000 @ 80% DoD

For marine, coastal, or harsh outdoor installs, Fortress eFlex Max 5.4 kWh battery delivers robust build, smooth integration, and long service life.

Why Choose the Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP Battery?

The Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP battery stands out due to its advanced engineering and user-focused design. It combines high energy density with exceptional thermal stability, making it a trusted choice for both residential and commercial energy storage systems.

Advanced Lithium Iron Phosphate Technology

LFP chemistry is known for its enhanced safety and longevity. Unlike traditional battery technologies, it minimizes the risk of overheating and thermal runaway. This ensures safer operation over thousands of charge and discharge cycles, even under continuous use.

High Energy Capacity with Consistent Output

With a nominal capacity of 5.4kWh, this battery provides sufficient energy storage to support essential appliances, lighting systems, and power tools. The 51.2V configuration ensures compatibility with a wide range of inverters and energy management systems, offering smooth integration into existing setups.

Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP Battery – eFlex Max 5.4 Performance Benefits

The Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP battery – eFlex Max 5.4 is engineered for efficiency and scalability. Its modular design allows users to expand storage capacity as energy demands grow, without compromising performance.

Long Cycle Life and Reduced Maintenance

This battery is designed to deliver thousands of cycles with minimal degradation. Compared to conventional batteries, it requires significantly less maintenance, helping users reduce long-term operational costs while enjoying reliable energy availability.

Smart Battery Management System (BMS)

An integrated BMS continuously monitors voltage, temperature, and current to protect the battery from overcharging, deep discharge, and short circuits. This intelligent system ensures optimal performance and extends the battery’s lifespan.

Ideal Applications for the Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP Battery

The versatility of the Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP battery makes it suitable for multiple applications:

Solar energy storage systems for storing excess solar power
Backup power solutions for homes and offices
Off-grid energy setups in remote locations
Commercial energy management to reduce peak demand charges

Its stable voltage output and fast response time ensure uninterrupted power during outages or high-demand periods.

Designed for Easy Installation and Scalability

Ease of installation is another advantage of this battery. The compact form factor allows flexible mounting options, while standardized connectors simplify system integration. For growing energy needs, multiple units can be connected in parallel to increase total storage capacity seamlessly.

The Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP battery is designed to adapt as energy requirements evolve, making it a future-ready investment.

Environmental and Economic Advantages

By utilizing clean energy storage, this battery supports reduced reliance on fossil fuels and promotes sustainable power usage. Its long lifespan and high efficiency translate into lower replacement frequency, reducing environmental impact and total cost of ownership.

For users focused on energy independence and sustainability, this battery offers a balanced solution that aligns performance with environmental responsibility.

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 Max 5.4 kWh battery — rugged 48 V LiFePO₄ (IP65)

Fortress eFlex Max 5.4 kWh battery comes with an outdoor-rated aluminum enclosure (IP65), 48 V/105 Ah LFP cells, and closed-loop inverter comms—for reliable performance in harsh climates.

Key features

Fortress eFlex Max 5.4 kWh battery offers high cycle-life (≈8,000 @ 80% DoD), >98% RTE, OTA updates, RS485/CAN, and flexible mounting options.

5.4 kWh energy · 48–55 V operating · 105 Ah capacity
Max charge 100 A · max discharge 60 A (cont.)
Aluminum IP65 case with improved thermal design
Wall/floor/rack mount; compatible with Envy & third-party 48 V inverters

Specifications

**Fortress eFlex Max 5.4 kWh battery** — specification box
Total energy	5.4 kWh
Nominal / operating V	48 V / 48–55 V
Capacity	105 Ah
Charge / discharge (cont.)	100 A / 60 A
Round-trip efficiency	>98%
Enclosure	IP65 aluminum; wall/floor/rack mount
Dimensions (L×W×H)	17.5″ × 24.2″ × 7.2″
Weight	≈108 lb
Temperature (charge / discharge)	32–114 °F / −4–131 °F
Cycle life	~8,000 @ 80% DoD

For marine, coastal, or harsh outdoor installs, Fortress eFlex Max 5.4 kWh battery delivers robust build, smooth integration, and long service life.

Why Choose the Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP Battery?

Advanced Lithium Iron Phosphate Technology

High Energy Capacity with Consistent Output

Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP Battery – eFlex Max 5.4 Performance Benefits

Long Cycle Life and Reduced Maintenance

Smart Battery Management System (BMS)

Ideal Applications for the Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP Battery

The versatility of the Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP battery makes it suitable for multiple applications:

Solar energy storage systems for storing excess solar power
Backup power solutions for homes and offices
Off-grid energy setups in remote locations
Commercial energy management to reduce peak demand charges

Its stable voltage output and fast response time ensure uninterrupted power during outages or high-demand periods.

Designed for Easy Installation and Scalability

The Fortress Power 105Ah 51.2V Nominal 5.4kWh LFP battery is designed to adapt as energy requirements evolve, making it a future-ready investment.

Environmental and Economic Advantages

For users focused on energy independence and sustainability, this battery offers a balanced solution that aligns performance with environmental responsibility.

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?

FAQs

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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!

Coll A

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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