Compare like with like. Aligned scores, specifications and local evidence within one scoring class or tier.
Market context
United States purchasing view
Fortress Power | eVault MAX 18.5; California Energy Commission listing eVaultMax
71/ 100
Strong evidence coverage · 100%
Evidence checked 2026-08-05
Available in United States · checked 2026-08-05
Buyer evidence: Ready (100% direct coverage).
BYD | Battery-Box Premium HVL 12.0 (US)
60/ 100
Strong evidence coverage · 100%
Evidence checked 2026-08-07
Available in United States · checked 2026-08-07
Buyer evidence: Ready (100% direct coverage).
| Measure | eVault MAX 18.5 | Battery-Box Premium HVL |
|---|---|---|
| Capacity & Usability | ||
| Power & Efficiency | ||
| Longevity (verified) | ||
| Safety & Chemistry | ||
| Guarantee & Backbone | ||
| Energy Ecosystem |
marks the better value on rows where a higher number is better. Temperature coefficient counts as higher when it is closer to zero. Size measures such as rated power carry no marker, because a larger product is a different choice rather than a better one.
| Measure | eVault MAX 18.5 | Battery-Box Premium HVL |
|---|---|---|
| Architecture | DC-coupled battery | DC-coupled battery |
| Published usable capacity range | 18.43 kWh | 12 kWh |
| Chemistry | LFP | LFP |
| Power | 9.2 kW | Not recorded |
| Round-trip | 98 % (better value on this row) | 96 % |
| Cycle life | 8,000 cycles | Not recorded |
| Evidence | eVault MAX 18.5 | Battery-Box Premium HVL |
|---|---|---|
| Outcome | Available in United States | Available in United States |
| Checked | 2026-08-05 | 2026-08-07 |
| Certifications | The California Energy Commission Battery List carries model eVaultMax under Fortress Power LLC, described as a 9.2 kW, 18.5 kWh lithium iron phosphate battery, UL 1973 certified by Intertek, with a listing date of 1 September 2021. The same model is on the Energy Storage System List under UL 9540., The datasheet lists UL1642, UL1973, UL9540 and UL9540A, and Fortress publishes the UL 9540A large-scale fire test letter, performed by TUV Rheinland, reporting that no external flaming was observed. Note the California Energy Commission record cites older certificate editions than the certificates Fortress currently publishes. | Exact HVL V1.9 datasheet: UL 9540A, UL 1973, IEC 60730, FCC and UN 38.3; UL 9540 applies only to exact certified system combinations |
| Warranty scope | United States; the warranty runs ten years or 8,000 cycles at 80% depth of discharge or 3,000 cycles at 100%, whichever comes first, with warranted throughput of 87.2 MWh at 80% DoD, 48.9 MWh at 90% and 36.3 MWh at 100%. It contains no retained-capacity guarantee. Installation, removal, shipping and reinstallation costs are excluded. Registration within 30 days of purchase is required to validate cover, and the warranty voids on commissioning below full charge, charging below 32 F, a non-approved charger, or continuous use below 32 F or above 90 F. Disputes go to single-arbitrator arbitration in the owner's home county. | United States for named HVL products installed on or after 1 November 2024; ten years or 30.30 MWh for HVL 12.0, whichever occurs first, with 70% retained usable energy. |
| Warranty remedy | The warranty supplies the stated product remedy until the earliest time, cycle or throughput limit; it does not guarantee retained capacity. | Repair, equivalent new or used replacement, or a formula-based partial refund at BYD's discretion. |
| Labour and reinstallation | Installation and other site labour are excluded. Removal and reinstallation costs are excluded. | No site-labour reimbursement entitlement is stated. No removal or reinstallation benefit is stated. |
| Freight | Shipping costs are excluded. | No ordinary freight entitlement is stated; transport damage is excluded. |
| Transfer and registration | The published warranty does not establish an unrestricted transfer right; a later owner should confirm eligibility with Fortress Power before purchase. Registration within 30 days of purchase is required, with commissioning, charger and operating-temperature conditions applying throughout the term. | Original Buyer only; no subsequent-owner transfer right is stated. No pre-registration is stated, but invoice, configuration, serial numbers, firmware and inverter details are mandatory for a claim. |
| Grid compatibility | A 48 V DC-coupled battery that reaches the grid only through a compatible inverter using closed-loop CAN or RS485 communication; Fortress's published residential packages pair it with the Envy True 12 hybrid inverter, and the California Self-Generation Incentive Program list also verifies pairings with Sol-Ark inverters. The installation manual mandates indoor installation. | 120-173 V DC operating range for HVL 12.0. AC transfer, grid forming and outage PV behavior depend on an exact certified inverter and system design. |
| Local product pathway | No separate local pathway recorded | No separate local pathway recorded |
| Buyer evidence | Ready (100% direct coverage): Local availability, buyer evidence, and the publication threshold are confirmed. | Ready (100% direct coverage): Local availability, buyer evidence, and the publication threshold are confirmed. |
| Safety notice | No model-specific notice recorded | No model-specific notice recorded |
| Review note | Fortress Power, LLC of 2010 Cabot Blvd West, Suite L, Langhorne, PA 19047, telephone 877-497-6937, is the named warrantor, describing itself in the warranty as the distributor and supplier. Fortress states its products are designed, engineered and inventoried in the United States with United States support, and told EnergySage its products are engineered and designed in the United States and assembled in Asia, with lithium iron phosphate cells from Asia, so this is not a made-in-USA product despite the Pennsylvania headquarters. The warranty document still prints a superseded Southampton, Pennsylvania address. Fortress operates a where-to-buy dealer locator. | BYD America LLC is the warrantor and publishes a US service route. The warranty is Original Buyer only and does not promise labour, freight, removal or reinstallation. |
| Sources | Source 1Source 2Source 3Source 4Source 5 | Source 1Source 2Source 3Source 4Source 5 |
A score lead is only meaningful inside this shared class or tier. Weigh it against the specification and evidence rows above before deciding.
Both products are scored in the Performance & Value class, on the same rubric weighting. Scores are not comparable across classes or tiers. Full methodology.