Fortress Power Batteries

Fortress Power Batteries: Solar Batteries Built for Hard Duty

Fortress Power makes 48V lithium iron phosphate storage for homes, cabins and small commercial sites, and its two lines answer two different questions. The eFlex Max is a 5.4kWh module you stack in multiples to reach the capacity you need, sealed to IP65 so it can hang in a garage, a barn or on an exterior wall. The eVault Max is a single 18.5kWh cabinet for whole-home backup where one large unit is simpler than four small ones. Both are solar batteries in the strict sense: they sit behind a hybrid inverter and store what your panels produce.

This collection holds the two Fortress batteries. The Fortress Power eFlex Max 5.4kWh 48V LFP Battery is in stock from $1,789. The Fortress Power eVault MAX 18.5kWh 48V LFP Battery lists at $6,349 and is currently sold out; call for restock timing.

How to choose between eFlex Max and eVault Max

• Capacity you need tonight. A home running a fridge, lights, internet and a furnace fan through the night uses roughly 5 to 10kWh. Two eFlex Max modules (10.8kWh) cover that; the eVault Max holds 18.5kWh in one box for homes with electric cooking or a heat pump.
• Where it will live. The eFlex Max carries an IP65 dust and water rating and an enclosure Fortress rates at four times the thermal performance of competing batteries, so an unconditioned garage or a covered outdoor wall is acceptable. The eVault Max is a floor-standing cabinet better suited to a utility room.
• Cycle life and warranty. The eFlex Max is rated for 8,000 cycles at 80% depth of discharge; the eVault Max for 6,000 or more at the same depth. Both carry a 10-year warranty.
• Inverter communication. Fortress batteries communicate over CAN and RS485 and are listed as compatible with Sol-Ark, Schneider and Victron inverters. Confirm the closed-loop profile for your specific inverter before ordering, because that is what makes state-of-charge readings accurate.
• Growth path. Modular eFlex units add 5.4kWh at a time; multiple eVault cabinets can be stacked for larger systems. If you expect to add an EV charger later, buy the inverter with headroom now and add battery modules when the need arrives.

Popular picks in this collection

Sizing tips

• Run the Solar Kit Calculator with your appliance list and ZIP code. It returns a battery size in kWh, which you then divide by 5.4 to get the number of eFlex Max modules.
• Size for usable energy, not nameplate. Fortress rates the eFlex Max at 5.374kWh at a 0.5C discharge; heavy loads drawn fast return a little less.
• Plan the discharge rate against your inverter. A 12kW inverter pulling full power from a single 5.4kWh module is a mismatch; three or four modules share the current and last longer.
• Cold matters. LiFePO4 will not charge below freezing, so an unheated shed in a northern state needs either a conditioned space or an enclosure that stays above 32F.
• If you are browsing fortress solar batteries for an existing Sol-Ark or Victron system, have the inverter firmware version handy when you call so we can confirm the communication setup.

Frequently asked questions

Can I mix eFlex Max and eVault Max on one inverter? Fortress designs each line to be paralleled with its own kind. Mixing capacities on one bus makes the battery management uneven, so choose one line and grow within it.

How many eFlex Max batteries do I need for a whole house? Most homes wanting overnight backup land on three to four modules, 16 to 22kWh. Homes with a well pump, electric range and heat pump should compare that against the 18.5kWh eVault Max once it is back in stock.

Are these fortress eflex lifepo4 batteries safe indoors? Lithium iron phosphate is the most thermally stable common lithium chemistry, and the eFlex enclosure is engineered specifically for heat management. Follow the manufacturer clearance guidance and local code for the installation location.

Fortress batteries ship free to the mainland US from brand partner warehouses, usually within a few business days, with 30-day returns. If you are comparing solar batteries for sale and want a second opinion on capacity, call us and we will size the bank with you.