Fortress Power 5.4kW Lithium Deep Cycle Lithium Solar Battery -
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SKU eFlex 5.4

Fortress Power eFlex 5.4kW Lithium Deep Cycle Solar Battery

Current price $3,185
Original price $3,950
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*Limited Supply. Order Yours Today!*

Quite possibly the most well made battery on the market, the eFlex 5.4 kWh lithium battery from Fortress Power comes with built-in wifi for remote monitoring and troubleshooting to compliment its 10 year warranty with the safe and premium prismatic Lithium-Iron-Phosphate cells.  It's expandable from 5.4 kWh to 81 kWh for whatever your application needs making this one of the most popular units in the Fortress line-up.



The aluminum cabinet that houses the high quality battery cells is IP 65 waterproof which will prevent salt water corrosion.


  • Total Energy: 5.376 kWh
  • Nominal Voltage: 51.2(48)V
  • Voltage Range: 45-58.4 V
  • Max. Charge Current(Continuous): 100 Amp
  • Max. Discharge Current(Continuous): 100 Amp
  • Recommend Storage temperature: 32 to 95 F
  • Charge temperature: 32 to 113 F
  • Capacity: 105 Amp-hour
  • Dimension(H x W x D): 7.2" x 17.5" x 21.5"
  • Weight: 116 lbs



Lowest cost per cycle!

High ound trip efficiency & >99% mixed with 6000+ lifecycles means that this is one of the best bangs for your buck when it comes to a lithium deep cycle battery. 


Fortress Power 5.4kW Lithium Deep Cycle Solar Battery Features:

High Durability and long-lasting: 10 Year Warranty with the safe and premium prismatic Lithium-Iron-Phosphate cells

Versatile Applications: Expandable from 5.4 kWh to 81 kWh for residential, commercial, railway, military and telecommunications applications

Lowest Cost Per Cycle: High energy throughout with exceptional life span (6000+ cycles) and hight round-trip efficiency (>99%)

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

Waterproof and saltwater resistant: The sleek-looking aluminum cabinet has IP65 waterproof rating to prevent salt-water corrosion

Fortress Power 5.4kW Lithium Deep Cycle Solar Battery Are Compatible with most inverters!

The eFlex5.4 is compatible with most inverters on the market today, but customers have found the best pairing with the units below:

- Sol Ark

- Outback Radian Series

- Schneider Conext

Fortress Power 5.4kW Lithium Deep Cycle Solar Battery Compatible Inverters

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. 

Sol-Ark: AC or DC coupled

 8 KW & 12 KW Inverters 

Schneider: AC or DC coupled

Conext XW MPPT charge controller; Conext XW+/XW pro series 

Outback: AC or DC coupled

Skybox, FLEX max charge controller (48V), FLEXpower series (48V); Radian series (48V); FXR(A) and FXR (E) series (48V); GVFX and GVFX series (48V); 

Magnum: AC or DC coupled

MS 4448PAE; MS 4048-20B 

SMA: AC coupled

SUNNY ISLAND 4548-US/6048-US; SUNNY ISLAND 3.0M/4.4M/6.0H/8.0H 

Victron: DC coupled

Phoenix VE.Direct Inverter; MultiPlus and Quatro Inverter/Charger; Skylla-TG Charger; General; Color Control or Venus GX 

Morning Star: DC coupled 

TriStar MPPT 600V; TriStar MPPT; Tristar PWM 

Midnite Solar: DC coupled

Solar Classic 150, 200 & 250; Solar Classic 150, 200 & 250-SL


*In Stock & Ready To Ship! Limited Supply. Order Yours Today!*

Still have questions? Give us a call at 877-242-2792


What is the Shop Solar Kits returns policy?

Returns are free in the first 30 days with no restocking or processing fees, although the customer must pay for the return shipping costs. See our complete return policy on our Shipping, Deliver, and Returns page.

What’s covered by the Shop Solar Kits returns policy?

Our returns policy covers all purchases made through Shop Solar Kits. 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 Shop Solar Kits order?

All orders are processed within 72 hours and you can expect delivery within 5 to 10 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 the financing and payment options at Shop Solar Kits?

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, see our Financing page for more details

How does the Shop Solar Kits Lifetime Support work?

Our legendary lifetime customer support has helped make us the #1 solar kit 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 Shop Solar Kits equipment, we’ve got you covered: we’re always only a phone call or email away.

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