Fortress Power eFlex MAX 5.4
A tough 5 kWh module for off-grid cabins, boats and small systems that need an outdoor-rated case. Larger inverters need three or more to run at full power.
Current Connected $1,449$1,449
The Fortress Power eFlex MAX 5.4 is the better 48V solar battery overall, rated 4.2 to 4.0. The Fortress Power eFlex MAX 5.4 costs $98.55 less ($1,449 vs $1,547.55).
Growatt ALP 5.0L-E2 US
An outdoor-rated 5 kWh battery for owners of a Growatt US hybrid inverter. Owners of other inverter brands get more for less from a rack module.
Amazon $1,547.55$1,547.55
Prices were last checked October 24, 2026 and are subject to change; the price and availability shown by the retailer at the time of purchase apply.
Scores side by side
Each factor is scored 0-100 against the same fixed reference points for every wall and floor mount 48V solar battery; a clear win is highlighted. How we rank explains each one.
| Factor weight | Fortress Power eFlex MAX 5.4 | Growatt ALP 5.0L-E2 US |
|---|---|---|
| Overall rating | 4.2/5 | 4.0/5 |
| Value 35% | 73 $270 per rated kWh | 66 $302 per rated kWh |
| Output 15% | 39 60 A continuous (about 3.1 kW) | 43 60 A continuous (about 3.1 kW) |
| Warranty 15% | 100 10-year warranty | 100 10-year warranty |
| Safety listing 15% | 100 UL 1973, UL 9540 listed | 100 UL 1973, UL 9540A listed |
| Cycle life 10% | 100 8,000 cycles at 80% depth, maker rating | 50 cycle life not published (neutral score used) |
| Features 10% | 70 inverter communication, app; no self-heating | 70 inverter communication |
Specifications
| Fortress Power eFlex MAX 5.4 | Growatt ALP 5.0L-E2 US | |
|---|---|---|
| Capacity | ||
| Case | Wall or floor mount | Wall or floor mount |
| Nominal voltage | 51.2 V | 51.2 V |
| Capacity | 105 Ah | 100 Ah |
| Energy | 5.4 kWh | 5.1 kWh |
| Usable energy | - | 4.6 kWh |
| Chemistry | LiFePO4 | LiFePO4 |
| Cycle life | 8,000 at 80% depth | - |
| Power | ||
| Continuous discharge | 60 A | 60 A |
| Peak discharge | 130 A | - |
| Max charge current | 100 A | 60 A |
| Modules in parallel | Up to 16 | Up to 8 |
| Safety and communication | ||
| UL 1973 | Yes | Yes |
| UL 9540A | Yes | Yes |
| UL 9540 | Yes | No |
| Communication | CAN, Modbus, Wi-Fi | CAN |
| Works with inverters | Fortress Envy, Schneider, Sol-Ark, Midnite Solar, OutBack, Morningstar, Phocos, Victron, Growatt | Growatt |
| Self-heating | No | - |
| App | Yes | - |
| Build | ||
| Display | No | - |
| Enclosure | IP65 | IP66 |
| Dimensions | 17.5 x 7.2 x 24.2 in (446 x 184 x 616 mm) | 28.0 x 7.3 x 11.6 in |
| Weight | 112 lb | 101.4 lb |
| Warranty | 10 years | 10 years |
| Released | 2024-05 | 2024-06 |