Illustrative equipment photography, not this model.
Fortress Power battery
The small Fortress, stackable and documented to the same standard as the eVault. You pay a premium per kilowatt hour for paperwork that actually names inverters.
Published figures
Usable capacity
5.4 kWh
Capacity
100 Ah
Voltage window
44.8 to 58.4 V
Max charge current
100 A
Max discharge current
100 A
Comms
CAN, RS485
Form factor
Wall or rack
Units in parallel
10
Source status: Provisional figure Typical street price $2,200 to $3,000. Charge and discharge limits are per unit. Wiring packs in parallel raises both.
How many you need, by inverter
One pack accepts 100 amps. An inverter that can deliver more than that needs more than one, or the charge rate capped in settings. Both are valid, and the second one costs you charging speed on the short days when you need it most.
Manufacturer documentation names Sol-Ark 12K, Sol-Ark 15K, Sol-Ark 8K for closed-loop operation with this pack.
Where the figures come from
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.
Where to buy the Fortress eFlex 5.4kWh
Listings for the Fortress eFlex 5.4kWh plus the rack hardware and cabling a clean install needs.
Affiliate 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.
Questions people actually ask
How many Fortress eFlex 5.4kWh packs do I need?
One pack accepts 100 amps and holds 5.4 kWh. Match the pack count to your inverter’s charge current first, then check the energy. A Sol-Ark 15K at 275 amps would take 3 of them to charge at full rate.
Does the Fortress eFlex 5.4kWh do closed loop communication?
