Checked as a bank of 2 packs, which is the smallest number that accepts this inverter’s 165 amp charge current. Fewer packs still run the system, with the charge rate capped in inverter settings.
Full specifications: Sol-Ark 8K and Fortress eVault Max 18.5kWh.
The four checks
Voltage window: Overlapping window 44.8 to 58.4 V
The inverter operates from 42 to 63 volts and the battery cuts off outside 44.8 to 58.4 volts. Both stay inside 44.8 to 58.4 volts, which covers a normal LiFePO4 charge and discharge cycle with margin at both ends.
Charge current: 165 A into a 266 A limit
The inverter tops out at 165 amps and the battery accepts 266 amps, so a default install cannot overrun the pack. Adding batteries in parallel raises the accepted current further.
Surge rating: 400 A surge for 5 s against a 250 A peak
The inverter surges to 12000 watts, about 250 amps at 48 volts, and the battery is rated for 400 amps for 5 s. A compressor or well pump start has room inside that rating. Compare the durations as well as the amps, because the ratings are only equivalent if the pack can hold its figure as long as the inverter holds its own.
Closed-loop communication: Named in a manufacturer document
A manufacturer document names this exact pairing for closed-loop operation over CAN, RS485. That is the only evidence this site accepts for a match on this check. Select the matching protocol profile in the inverter menu during commissioning.
What this means when you install it
Set the inverter charge current to 165 amps or less. That is the inverter maximum, which this bank can absorb. Protect the battery run with a 250 amp Class T fuse and 4/0 AWG cable wired to a busbar rather than daisy chained, so all 2 packs share current evenly.
A manufacturer document names this exact pairing for closed-loop operation over CAN, RS485. That is the only evidence this site accepts for a match on this check. Select the matching protocol profile in the inverter menu during commissioning.
Figures side by side
| Field | Sol-Ark 8K | Fortress eVault Max 18.5kWh |
|---|---|---|
| Voltage window | 42 to 63 V | 44.8 to 58.4 V |
| Charge current | 165 A delivered | 266 A accepted (2 packs) |
| Peak draw | 12,000 W surge | 400 A surge (2 packs) |
| Usable capacity | n/a | 37.0 kWh (2 packs) |
| Comms | CAN, RS485 | CAN, RS485 |
Manufacturer documents
Manufacturer documents: Sol-Ark resources and manuals. Figures here should be read against the revision that covers your serial number, because manufacturers revise specifications without changing the model name.
Manufacturer documents: Fortress Power document library. Figures here should be read against the revision that covers your serial number, because manufacturers revise specifications without changing the model name.
Both units, current pricing
Prices on these move week to week, and the battery is usually the line item worth watching.
Sol-Ark 8K on AmazonFortress eVault Max 18.5kWh on AmazonComms cableAffiliate links. As an Amazon Associate this site earns from qualifying purchases, at no extra cost to you. Prices and stock change often, and a listing appearing here is not a statement that the pairing above is approved.
Other pairings for the Fortress eVault Max 18.5kWh
EG4 18KPV with Fortress eVault Max 18.5kWh
Partial match, some fields unverified.
Sol-Ark 12K with Fortress eVault Max 18.5kWh
Specs align on every checked field.
Sol-Ark 15K with Fortress eVault Max 18.5kWh
Specs align on every checked field.
Victron MultiPlus-II 48/5000 with Fortress eVault Max 18.5kWh
Specs align on every checked field.
Questions people actually ask
Will the Sol-Ark 8K work with the Fortress eVault Max 18.5kWh?
Specs align on every checked field. Checked as a bank of 2 packs, which is the smallest number that accepts this inverter’s 165 amp charge current. Fewer packs still run the system, with the charge rate capped in inverter settings. The four checks below show which field produced that result.
What does this pairing cost to wire up?
Beyond the two units, a 250 amp Class T fuse and holder, 4/0 AWG battery cable cut to matched lengths, and a busbar if you are running 2 packs. A comms cable if you intend to attempt closed loop, and the pinout is rarely the same between brands.
Where does this pairing go wrong in practice?
A manufacturer document names this exact pairing for closed-loop operation over CAN, RS485. That is the only evidence this site accepts for a match on this check. Select the matching protocol profile in the inverter menu during commissioning.
What charge current should I set?
The inverter tops out at 165 amps and the battery accepts 266 amps, so a default install cannot overrun the pack. Adding batteries in parallel raises the accepted current further.