Fortress Power
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Housed in a saltwater-proof, IP65 aluminum enclosure, the Fortress Power eFlex MAX is a 48V 105Ah LiFePO4 battery storing 5.4kWh. It suits residential backup, solar self-consumption, off-grid systems, and RVs and boats.
Planning a system? Read our guide: How to size a battery backup system for your home.
Indoor or outdoor home storage and mobile systems, including RVs and boats.
Fortress Power eFlex MAX 5.4kWh LFP Battery The Fortress Power eFlex MAX 5.4 is a compact 48V lithium iron phosphate battery designed for residential backup, solar self-consumption, off-grid systems, and mobile applications like RVs and boats. It stores 5.4kWh of usable energy at 51.2V nominal with a 105Ah capacity, and supports continuous charge and discharge currents of 55A and 60A respectively. The eFlex MAX achieves up to 98% round-trip efficiency with just 2W of idle consumption, making it one of the more efficient options on the market for both grid-tied and off-grid use. It ships with communication cables, a Flex Max Top Cover, and threaded conduit fittings. Wall mount bracket and busbar are sold separately. Cell Chemistry and Cycle Life The eFlex MAX uses Tier-1 automotive prismatic lithium iron phosphate cells rated for over 8,000 cycles at 80% depth of discharge. At one full cycle per day, that works out to over 21 years of expected service before the battery reaches its end-of-life capacity threshold. Fortress Power backs the eFlex MAX with a 10-year warranty. Built for Harsh Environments Fortress Power engineered the eFlex MAX with a patented aluminum enclosure that is saltwater-proof and IP65 rated against dust and water ingress. This means the battery can be installed indoors or outdoors without requiring an additional protective enclosure. The aluminum shell provides four times better thermal performance than competing designs, which helps maintain cell health during sustained high-power loads and temperature extremes. The charging temperature range is 32°F to 114°F, with a discharge range of -4°F to 131°F and a storage range of 20°F to 95°F. Battery Management System The onboard digital processor BMS monitors individual cell voltage and temperature with active balancing, keeping cells healthy and extending the battery’s usable life. It includes an integrated 125A breaker, overcharge and deep discharge protection, and short circuit safeguards. Idle power consumption is just 2W, which is an important detail for off-grid systems where every watt counts. Communication and Inverter Compatibility The eFlex MAX supports CAN bus and Modbus communication protocols with OTA firmware updates and remote monitoring. Advanced closed-loop communication allows seamless integration with most 48V inverters, including Fortress Power Envy, Sol-Ark, Victron, and others. This closed-loop integration gives the inverter real-time visibility into battery voltage, current, temperature, and state of charge for optimized charging and discharging. Scalability A single eFlex MAX provides 5.4kWh of storage. For larger systems, up to 16 units can be connected in parallel for a maximum capacity of 86kWh. The optional busbar package simplifies paralleling by supporting higher current loads and reducing wiring complexity. Installation and Mounting The eFlex MAX supports wall mount, floor stand, and 19-inch industrial server rack configurations, giving installers flexibility for a wide range of site conditions. The included Flex Max Top Cover and threaded conduit fittings provide clean, code-compliant cable routing. A waterproof front cover keeps connections protected in outdoor installations.
Warranty terms mentioned in this description are the manufacturer’s. Our own coverage is the 30-day limited warranty.
We confirm compatibility, installation requirements, and delivery details with you during order review, before any payment. Home electrical work may require a qualified installer.
Ask our team whether the eFlex MAX communicates with your inverter. Message our team on WhatsApp.
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