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 3.8. The Fortress Power eFlex MAX 5.4 leads on safety listing and features. The SunGoldPower CoreX 5 Elite wins on output. The SunGoldPower CoreX 5 Elite costs $199 less ($1,250 vs $1,449).
SunGoldPower CoreX 5 Elite
The wall-mount version of the CoreX 5 Pro, for indoor systems where a rack doesn’t fit. Choose a UL-listed battery if your permit needs one.
Amazon $1,250$1,250
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.
Which should you buy?
- Choose the Fortress Power eFlex MAX 5.4 for safety listing (UL 1973, UL 9540 listed vs no UL listing) and features (inverter communication, app; no self-heating vs app; no self-heating).
- Choose the SunGoldPower CoreX 5 Elite for output (100 A continuous (about 5.1 kW) vs 60 A continuous (about 3.1 kW)).
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 | SunGoldPower CoreX 5 Elite |
|---|---|---|
| Overall rating | 4.2/5 | 3.8/5 |
| Value 35% | 73 $270 per rated kWh | 79 $244 per rated kWh |
| Output 15% | 39 60 A continuous (about 3.1 kW) | 100 100 A continuous (about 5.1 kW) |
| Warranty 15% | 100 10-year warranty | 100 10-year warranty |
| Safety listing 15% | 100 UL 1973, UL 9540 listed | 0 no UL listing |
| Cycle life 10% | 100 8,000 cycles at 80% depth, maker rating | 40 5,000 cycles at 100% depth, maker rating |
| Features 10% | 70 inverter communication, app; no self-heating | 50 app; no self-heating |
Specifications
| Fortress Power eFlex MAX 5.4 | SunGoldPower CoreX 5 Elite | |
|---|---|---|
| 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 |
| Chemistry | LiFePO4 | LiFePO4 |
| Cycle life | 8,000 at 80% depth | 5,000 at 100% depth |
| Power | ||
| Continuous discharge | 60 A | 100 A |
| Peak discharge | 130 A | - |
| Max charge current | 100 A | 95 A |
| Modules in parallel | Up to 16 | Up to 15 |
| Safety and communication | ||
| UL 1973 | Yes | No |
| UL 9540A | Yes | No |
| UL 9540 | Yes | No |
| Communication | CAN, Modbus, Wi-Fi | CAN, RS485 |
| Works with inverters | Fortress Envy, Schneider, Sol-Ark, Midnite Solar, OutBack, Morningstar, Phocos, Victron, Growatt | - |
| Self-heating | No | No |
| App | Yes | Yes |
| Build | ||
| Display | No | Yes |
| Built-in breaker | - | Yes |
| Enclosure | IP65 | IP20 |
| Dimensions | 17.5 x 7.2 x 24.2 in (446 x 184 x 616 mm) | 22.05 x 18.9 x 5.39 in |
| Weight | 112 lb | 105.8 lb |
| Warranty | 10 years | 10 years |
| Released | 2024-05 | 2026-04 |