Category:
Batteries
Fortress Power eVault Max: Full Specs, Pricing & Honest Review (2026)
Brand:
Fortress Power
Quick Verdict
The eVault Max is Fortress Power's large-capacity residential and light-commercial battery, notable for its high round-trip efficiency (over 98%) and serious scalability — up to 370 kWh when multiple units are stacked. It works with both AC and DC coupling, giving installers flexibility across different system types.
One important note: Fortress Power has indicated the eVault Max is being phased out in favor of newer eBoost models, so availability may be limited going forward.
Best for: Larger installations or off-grid setups needing significant scalable capacity, where a value-oriented LFP battery makes sense.
Conceptual illustration of a stackable home battery cabinet (not the actual product)
Product image is a conceptual illustration for reference purposes only and does not depict the actual manufacturer product. Specifications are sourced from official manufacturer datasheets.
Key Features
18.5 kWh capacity per unit, scalable to 370 kWh
Over 98% round-trip efficiency
AC/DC coupled — flexible integration with various inverter brands
Serviceable top cover for straightforward maintenance access
Key Specs
Usable Capacity: | 18.5 kWh (per unit) |
Coupling: | AC/DC coupled |
Chemistry: | LFP (prismatic Lithium Iron Phosphate cells) |
Round-Trip Efficiency: | >98% |
Warranty: | 10 years, or 6,000 cycles at 80% DOD / 2,000 cycles at 100% DOD |
Scalability: | Up to 370 kWh (multiple units) |
Monitoring: | Closed-loop communication with compatible hybrid inverters |
Note: Fortress Power has signaled the eVault Max is being phased out in favor of the newer eBoost line. Confirm current availability with your installer before specifying this model for a new install.
Price Range
Typical unit price: $9,000–$10,500 for the battery alone, before installation.
Note: Pricing varies by installer, region, and system configuration. These are general market ranges, not a quote. ElecGuys doesn't sell equipment directly. Given the phase-out noted above, confirm current pricing and stock before relying on this figure.
Pros
Very high round-trip efficiency (>98%), among the best in this category
Large per-unit capacity (18.5 kWh) with serious scalability for bigger systems
Flexible AC/DC coupling accommodates different inverter setups
Competitive pricing relative to capacity compared to Tesla or FranklinWH
Cons
Being phased out by the manufacturer in favor of newer eBoost models — long-term parts/support availability is uncertain
Shorter round-trip efficiency track record publicly available compared to more established brands
Less brand recognition among California homeowners than Tesla or Enphase
FAQ
Q: Is the eVault Max still a good choice for a new installation?
A: Worth discussing directly with your installer first. Fortress Power has indicated this model is being phased out in favor of their newer eBoost line, so confirm current availability, warranty support, and whether the eBoost is a better fit before specifying it for a new system.
Q: What does AC/DC coupled flexibility mean in practice?
A: It means the eVault Max can be configured to work either as a DC-coupled battery (paired directly with a compatible solar charge controller) or AC-coupled (added onto an existing inverter setup), giving installers more design flexibility than single-coupling-type batteries.
Q: How does 98% round-trip efficiency compare to competitors?
A: It's at or near the top of the category — most LFP home batteries land in the 90-95% range, so the eVault Max's efficiency edge can meaningfully reduce energy losses over the system's lifetime.
Related Post
[No dedicated ElecGuys battery post yet — see note below]