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Resource Center · by CSE Solar USA
The Fortress Power Energy Storage Resource Center
LiFePO4 batteries, hybrid inverters and all-in-one backup — genuine Fortress Power, stocked and supported in the U.S. with fast nationwide shipping.
- Authorized Fortress Power Distributor
- Inverters
- Batteries
- Commercial
- DIY & Off-Grid
- Enclosures
Featured systems
Ready-to-ship Fortress bundles
Popular Solo 6.5K pairings for DIY, off-grid and compact spaces — in stock and supported by CSE Solar USA.
Why Fortress Power
How Fortress compares
Real specs from Fortress Power’s battery and system comparison charts — built to outperform on capacity, cycles, safety and cost.
System comparison · Envy Duo 21 backup systems
| Spec | Envy Duo 21 + eBoost | Envy Duo 21 + eForce | Competitor #1 |
|---|---|---|---|
| Max PV input | 25 kW | 25 kW | 20 kW |
| Energy storage | 16.1 kWh | 19.2 kWh | 13.5 kWh |
| Continuous AC output | 16 kW | 16 kW | 11.5 kW |
| Backup power | 12 kW | 12 kW | 11.5 kW |
| Surge | 24 kW | 24 kW | 185 LRA |
| Efficiency | 96.9% CEC | 96.9% CEC | 89% |
| Warranty | 10 yr · 8,000 cycles | 15 yr · 8,000 cycleswith Guardian | 10 yr |
| Generator compatible | Yes | Yes | No |
| Serviceable | Yes | Yes | No |
| Flexible to scale | Yes | Yes | No |
| Levelized cost of energy | $0.22/kWh | $0.19/kWh | $0.38/kWh |
Battery comparison · eFlex MAX 5.4 vs other 5 kWh rack batteries
| Feature | Fortress eFlex MAX 5.4 | Other 5 kWh rack batteries |
|---|---|---|
| Nominal capacity | 5.4 kWh | 5.1 kWh |
| Code-compliant install | Yessleek, integrated | Noenclosure needed |
| Saltwater-proof | Yesaluminum enclosure | Nosteel case |
| Outdoor rated | Yes | No |
| Cycles | 8,000 @ 80% DoD | 6,000 @ 80% DoD |
| Warranty | 10 years | 5 or 10 years |
| Years on market | 7 yrs · 0.1% cell failure | 3 yrs |
Real product, real support
An authorized distributor that actually knows the product
CSE Solar USA has been in solar since 2008. As an authorized Fortress Power distributor we deliver genuine product with full manufacturer warranty, real technical support, and fast U.S. fulfillment, shipped nationwide.
Whether you’re a DIY homeowner setting up a Solo 6.5K, an installer specifying an Envy Duo 21 system, or a business sizing eSpire Nano commercial storage, we help you choose the right Fortress configuration and back it after the sale.
Talk to a specialist: (702) 608-8385 — or request a quote and we’ll spec it for you.
Why it stands out
- Safe LiFePO4 chemistry, 8,000-cycle rating
- 96.9% CEC efficiency on Envy systems
- Outdoor-rated, saltwater-proof enclosures
- Up to 15-year warranty with Guardian
- Generator-ready, scalable & serviceable
Product families
Shop the Fortress Power range
Fortress’s full catalog runs 36 SKUs — here are the systems CSE stocks. Filter by family.
In stock
Inverters · Off-Grid
Solo 6.5K Off-Grid Inverter
Non-export off-grid inverter — the heart of affordable DIY & whole-home backup.
Request a quote
In stock
Inverters · Hybrid
Envy Duo 21 Inverter
Flexible hybrid for residential & light-commercial — grid-tied, off-grid & generator-backed.
Request a quote
In stock
Inverters · Hybrid
Envy True 12kW Inverter
True 12 kW hybrid inverter for larger homes and demanding loads.
Request a quote
In stock
Inverters · Hybrid
Envy 8kW Hybrid Inverter
8 kW hybrid inverter for residential solar-plus-storage.
Request a quote
In stock
Inverters · Hybrid
Envy 10kW Hybrid Inverter
10 kW hybrid inverter for larger residential systems.
Request a quote
In stock
Batteries
eBoost Scalable Battery (16 kWh)
16 kWh scalable LFP system — stack up to 9 modules across 3 Envy inverters.
Request a quote
In stock
Batteries
eForce Stackable Whole-Home Battery
Stackable whole-home LFP storage in 9.6 / 19.2 / 28.8 kWh configurations.
Request a quote
In stock
Batteries
eVault MAX 18.5 kWh Battery
High-capacity floor-standing LFP battery for whole-home & commercial backup.
Request a quote
In stock
Batteries
eFlex MAX 5.4 kWh Battery
Modular 5.4 kWh LFP — outdoor-rated, saltwater-proof, 8,000-cycle rating.
Request a quote
In stock
Batteries
eFlex 5.4 kWh LFP Battery
Modular 5.4 kWh LiFePO4 battery — stack to scale capacity.
Request a quote
In stock
Commercial · All-in-One
eSpire Nano
Turnkey outdoor BESS for small-to-mid commercial — scalable, sub-10-minute commissioning, integrated controls.
Request a quote
In stock
Commercial · All-in-One
eSpire Mini
Fully integrated turnkey BESS, 81–266 kWh per unit — 3-phase 208/480 Vac, outdoor-rated, UL 9540A.
Request a quote
In stock
Commercial · Flagship
eSpire 306
Flagship liquid-cooled system — 305.5 kWh/unit, scalable to 6.1 MWh, with grid support, peak shaving & backup.
Request a quote
In stock
Monitoring
Guardian Gateway
System monitoring & commissioning gateway — extends warranty to 15 years on eForce.
Request a quote
In stock
Inverters · Off-Grid
Solo 6.5K Off-Grid Inverter
Non-export off-grid inverter — the heart of affordable DIY & whole-home backup.
Request a quote
In stock
Inverters · Hybrid
Envy Duo 21 Inverter
Flexible hybrid for residential & light-commercial — grid-tied, off-grid & generator-backed.
Request a quote
In stock
Inverters · Hybrid
Envy True 12kW Inverter
True 12 kW hybrid inverter for larger homes and demanding loads.
Request a quote
In stock
Inverters · Hybrid
Envy 8kW Hybrid Inverter
8 kW hybrid inverter for residential solar-plus-storage.
Request a quote
In stock
Inverters · Hybrid
Envy 10kW Hybrid Inverter
10 kW hybrid inverter for larger residential systems.
Request a quote
In stock
Batteries
eBoost Scalable Battery (16 kWh)
16 kWh scalable LFP system — stack up to 9 modules across 3 Envy inverters.
Request a quote
In stock
Batteries
eForce Stackable Whole-Home Battery
Stackable whole-home LFP storage in 9.6 / 19.2 / 28.8 kWh configurations.
Request a quote
In stock
Batteries
eVault MAX 18.5 kWh Battery
High-capacity floor-standing LFP battery for whole-home & commercial backup.
Request a quote
In stock
Batteries
eFlex MAX 5.4 kWh Battery
Modular 5.4 kWh LFP — outdoor-rated, saltwater-proof, 8,000-cycle rating.
Request a quote
In stock
Batteries
eFlex 5.4 kWh LFP Battery
Modular 5.4 kWh LiFePO4 battery — stack to scale capacity.
Request a quote
In stock
Commercial · All-in-One
eSpire Nano
Turnkey outdoor BESS for small-to-mid commercial — scalable, sub-10-minute commissioning, integrated controls.
Request a quote
In stock
Commercial · All-in-One
eSpire Mini
Fully integrated turnkey BESS, 81–266 kWh per unit — 3-phase 208/480 Vac, outdoor-rated, UL 9540A.
Request a quote
In stock
Commercial · Flagship
eSpire 306
Flagship liquid-cooled system — 305.5 kWh/unit, scalable to 6.1 MWh, with grid support, peak shaving & backup.
Request a quote
In stock
Monitoring
Guardian Gateway
System monitoring & commissioning gateway — extends warranty to 15 years on eForce.
Request a quote
Fortress Power eVault MAX 18.5kWh | 48V LFP Battery
available For add ons only, Delivery 3-4 months.
Warranty: 10 Years
Fortress Power Envy True 12kW All-In-One Hybrid Inverter
-
Max PV Input: 21,000 W (600V Max Voc)
-
MPPT Trackers: 3 Independent MPPTs
-
Battery Voltage: 48V Nominal (40-60V Range)
-
Max Battery Charge/Discharge: 250 A
-
Surge Power: 20,000 VA (500ms) / 16,000 VA (5 mins)
-
Grid Pass-Through: 200 A
-
Efficiency: 97.5% (Max) / 96.5% (CEC Weighted)
Fortress Power Envy 8kW Hybrid Inverter
-
Max PV Input: 13,000 W (600V Max Voc)
-
MPPT Trackers: 2 Independent MPPTs
-
Battery Voltage: 48V Nominal (40-60V Range)
-
Max Battery Charge/Discharge: 167 A
-
Surge Power: 16,000 VA (500ms)
-
Grid Pass-Through: 60 A
-
Efficiency: 97.5% (Max) / 96.5% (CEC Weighted)
- Warranty: 10 Years
Fortress Power DuraRack – Indoor / Outdoor Enclosure
-
Max Energy Capacity: 21.6 kWh (using 4 x eFlex 5.4)
-
Busbar Rating: 500 A
-
Cable Gauge: 4/0 AWG (Main Output) / 4 AWG (Battery Cables)
-
Cooling: 48V DC Fan (Thermostat Controlled)
-
Knockouts: Multiple conduit entry points on sides and bottom
-
Door: Hinged with Key Lock
- Warranty: 3 Years
Fortress Power Guardian Gateway Battery Monitor
-
Power Consumption: ~5W
-
Communication Ports: CAN bus (Battery), Modbus TCP/RTU
-
Wireless: Wi-Fi 802.11 b/g/n (2.4 GHz) + Bluetooth 4.0 (for setup)
-
Wired Connection: Ethernet RJ45
-
AC Adapter: Input 100-240V AC / Output 24V DC
-
DC Input: 48V (Direct connection to battery terminals)
Fortress Power ESpire Mini 30kW Inverter & 81kWh LFP Battery ESS
-
AC Output Power: 30kW
-
Battery Capacity: 81 kWh
-
Max PV Input: Up to 135 kW (DC Coupled models)
-
Transfer Time: < 20ms (UPS Grade)
-
Round Trip Efficiency: > 90%
Not sure what you need?
Find your Fortress system
Use Fortress Power’s System Recommendation Tool right here on our site to get a battery and inverter combination matched to your project, then bring the result to our team to finalize.
Find your Fortress system
This tool opens best in its own tab. Answer 4 quick steps, then bring the result to our team and we’ll finalize your system.
Results are estimates for reference only. Consult the CSE Solar USA & Fortress Power teams for final system design.
Solutions
Residential & commercial
The same safe LiFePO4 storage, matched to the job.
Residential & DIY
Whole-home & off-grid backup
Solo 6.5K and Envy Duo 21 systems with eBoost, eForce or eFlex keep the lights on during outages and store your solar for the evening.
- Affordable, scalable, generator-ready
- Grid-tied, off-grid or backup configurations
- Built for homes, apartments & compact spaces
Commercial
eSpire Nano for commercial projects
Compact all-in-one storage for small-to-mid commercial — scalable capacity, streamlined commissioning and integrated controls in one solution.
- All-in-one architecture, flexible configurations
- Simplified project planning & deployment
- Distributor pricing & sizing support for bids
Commercial & Industrial
Scalable storage from 40 kWh to 6.1 MWh
Fortress Power fills the gap between residential products and utility-scale systems — turnkey, modular eSpire systems for businesses, facilities and critical infrastructure, sourced through CSE Solar USA.
- Turnkey outdoor BESS
eSpire Nano
Turnkey outdoor BESS — 40/60 kWh battery with 30/60 kW inverters, guided commissioning in under 10 minutes, 10-year warranty.
- Light commercial
eSpire Mini
Fully integrated turnkey solution, 81–266 kWh per unit, for large residential and light commercial (3Ph 208/480Vac).
- Up to 6.1 MWh
eSpire 306
Flagship liquid-cooled system — 305.5 kWh per unit, scalable to 6.1 MWh, with 98% efficiency and 10,000-cycle modules.
eSpire Nano — fuel & EV charging site
eSpire Nano — fuel & EV charging site
Solar array
Auto Dealerships Absorb DC fast-charger demand spikes; earn via V2G and demand-response programs.
Manufacturing
Eliminate demand charges (often 30–50% of the bill); ride through outages via microgrid.
Agriculture
Protect crops and irrigation during outages; pair with generators for remote off-grid.
Quick-Serve Restaurants
Prevent food spoilage with instant backup; cut costs with demand management.
Retail
Peak shaving and time-of-use savings, plus VPP and demand-response revenue.
Schools & Universities
Lower demand charges, back up campus operations, and tap grant funding.
Commercial & IndustrialKeystone EMS
One platform for solar, storage, EV & generators
The Keystone Energy Management System unifies your assets for lower energy costs, greater reliability and total control — across a single site or a multi-site portfolio.
- Affordable, scalable, generator-ready
- Grid-tied, off-grid or backup configurations
- Built for homes, apartments & compact spaces
- Affordable, scalable, generator-ready
- Grid-tied, off-grid or backup configurations
- Built for homes, apartments & compact spaces
40 kWh – 6.1 MWh
eSpire family capacity range
820 kWh
eSpire + 700 kW solar at Team Toyota
~50%
monthly bill cut at Chick-fil-A · ≈2.5-yr payback
Watch & learn
Video hub
Official Fortress Power product walkthroughs, features and installs — straight from the manufacturer’s channel.
Single-phase Hybrid Inverter| HYS-LV-USG1& DTS Installation
Inverters · Promo
When Home Needs Power Most, HiBattery Is There 💙
Inverters · Promo
Introduce Hione - Sustainable Living, Simplified by Hione.
Inverters · Promo
MiT — First ever 5000 W output microinverter
Inverters · Promo
Single-phase AC-coupled Inverter HAS-LV-USG1&DTS Installation
Inverters · Promo
Open Energy for All
Inverters · Promo
Solo 6.5K Inverter
Inverters · Promo
Envy Duo 21 Inverter
Inverters · Promo
Envy True 12K Inverter
Inverters · Promo
eBoost Battery
Batteries · Promo
eForce Features
Batteries · Features
eVault MAX
Batteries · Promo
eFlex MAX
Batteries · Promo
eSpire Nano
Commercial · Promo
eSpire Commercial Storage
Commercial · Overview
Envy True 12K Installation
Install & Setup
eBoost Unboxing & Install
Install & Setup
eFlex MAX Installation
Install & Setup
Guardian Gateway Commissioning
Install & Setup
Solo 6.5K Inverter
Inverters · Promo
Envy Duo 21 Inverter
Inverters · Promo
Envy True 12K Inverter
Inverters · Promo
eBoost Battery
Batteries · Promo
eForce Features
Batteries · Features
eVault MAX
Batteries · Promo
eFlex MAX
Batteries · Promo
eSpire Nano
Commercial · Promo
eSpire Commercial Storage
Commercial · Overview
Envy True 12K Installation
Install & Setup
eBoost Unboxing & Install
Install & Setup
eFlex MAX Installation
Install & Setup
Guardian Gateway Commissioning
Install & Setup
Learning Center
Guides & how-tos
Hosted on CSE Solar USA — practical reading for homeowners, DIYers and installers choosing Fortress Power.
Compare
eFlex MAX vs eFlex 5.4
What the MAX upgrade adds: outdoor rating, cycles and enclosure.
Inverters
Envy Duo 21 system guide
16 kW output, 96.9% CEC, grid-tied & off-grid explained.
Monitoring
Guardian gateway & warranty
Set up monitoring and extend coverage to 15 years.
Safety
Why LiFePO4 & outdoor rating
Saltwater-proof enclosures and 8,000-cycle chemistry.
FAQ
Frequently asked questions
Quick answers for homeowners, DIYers and installers.
Can a Fortress system power my whole home?
With the right inverter and enough battery capacity, yes. An Envy Duo 21 with eBoost (16.1 kWh) or eForce (19.2 kWh) delivers 16 kW continuous and 12 kW backup — we’ll size it to your loads.
Is LiFePO4 safe, and can it go outdoors?
Fortress uses LiFePO4 chemistry rated to 8,000 cycles. The eFlex MAX is outdoor-rated and saltwater-proof with an aluminum enclosure, so it doesn’t need a separate code-compliant box like many competitors.
Can I install a Solo 6.5K system myself (DIY)?
The Solo 6.5K is built for DIY and off-grid customers. We can supply complete Solo 6.5K + eFlex MAX or eBoost setups and point you to Fortress’s install videos — always follow local code and permitting.
What's the difference between eBoost, eForce and eFlex?
eFlex / eFlex MAX are modular 5.4 kWh batteries; eBoost is a 16 kWh scalable system; eForce is stackable whole-home storage (9.6–28.8 kWh); eVault MAX is an 18.5 kWh high-capacity unit. Use the tool above or call us and we’ll match it to your needs.
Do you offer installer / volume pricing?
Yes — active installer accounts get distributor-level pricing and priority technical support across the Fortress range.
What does the Guardian gateway add?
Guardian provides system monitoring and commissioning and extends the eForce warranty to 15 years (8,000 cycles). It’s part of the recommended ecosystem on larger systems.
What enclosures and accessories are available?
Fortress offers DuraRack, DuraRack Mini and FlexTower enclosures plus wall-mount kits and the eFlex MAX heat mat kit. We’ll spec the right enclosure for your battery configuration.
Are the systems generator-compatible and serviceable?
Yes — Envy Duo 21 systems are generator-compatible, outdoor-rated, wall-mountable, and both inverter and battery are field-serviceable. Confirm specifics and local code with our team.
