Fortress Power eVault Max 18.5
The eVault Max 18.5 is one of the largest single residential LFP batteries available, with full 100 percent depth of discharge and a 10 year, 8,000 cycle warranty, and it scales to 370 kWh. It is a DC storage module only, so its 9.2 kW continuous and 12 kW peak ratings assume a properly sized paired inverter, and the published 98 percent figure is a cell efficiency at 0.5C, not a certified AC round trip number.
Specifications
- Chemistry
- LFP
- Usable capacity
- 18.43 kWh
- Continuous power
- 9.2 kW
- Peak power
- 12 kW
- Round-trip efficiency
- 98%
- Depth of discharge
- 100%
- Warranty
- 10 year warranty, rated for 8,000 cycles at 80 percent depth of discharge
- Scalable to
- Up to 370 kWh, 20 modules in parallel
- Backup scope
- Whole-home capable
- Inverter
- Needs a separate inverter
- Weight
- 520 lb
- Dimensions
- 20.3 x 20.3 x 42.2 in
Efficiency basis: Datasheet lists 98 percent efficiency measured at 0.5C, which is a cell-level charge and discharge figure and not a full AC round trip rating. Round-trip numbers are only comparable across brands when measured the same way, so read the basis before comparing.
Source: Fortress Power eVault Max 18.5 Technical Datasheet. Specs verified 2026-07-01. Figures are per single unit at beginning of life; confirm the current datasheet with your installer.
Specs do not tell you if it pays off.
Payback depends on your rate plan, usable capacity, and local incentives, not the brand on the box.
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