Fox ESS EVO 10 vs Sunsynk L5.1 with ECCO inverter
Fox ESS EVO 10 stores 9.73 kWh per unit, expanding to 29.18 kWh. Sunsynk L5.1 with ECCO inverter stores 4.61 kWh per unit. Across the setups we list, continuous power is 5–10 kW for the EVO 10 and 3.6–5 kW for the L5.1 with ECCO inverter. Warranty: 12 years vs 10 years. Intelligent Octopus Flux: EVO 10 is “Sold by Octopus for this tariff; not on its FAQ list”; L5.1 with ECCO inverter is “Not on Octopus's list”.
Figures from manufacturer documents, last checked 26 Sept 2026. We don't rank products or take payment for results.
How they're built
Fox ESS EVO 10
All-in-one: battery with built-in hybrid inverter (solar connects on the DC side).
Backup: Built-in EPS (backup) output.
Sunsynk L5.1 with ECCO inverter
48 V low-voltage battery modules with a Sunsynk ECCO hybrid inverter; the inverter supports DC or AC coupling to existing solar.
Side by side
| Specification | Fox ESS EVO 10 | Sunsynk L5.1 with ECCO inverter |
|---|---|---|
| Usable capacity (per unit) | 9.73 kWhcalculatedCalculated; the datasheet gives total energy and depth of discharge, not usable energyFox ESS datasheet, p.2, Battery Connection | 4.61 kWhPer module, 90% depth of dischargeSunsynk datasheet, p.2 |
| Battery chemistry | LFP (LiFePO₄)Fox ESS datasheet, p.2 | LFP (LiFePO₄)Sunsynk datasheet, p.2 |
| Maximum usable storage (expanded) | 29.18 kWhcalculatedCalculated from parallel limit and usable capacityFox ESS datasheet | Not documented |
| How it expands | Up to 3 EVO units in parallelFox ESS datasheet, p.2, EPS output: Parallel operation | Up to 32 modules in parallel (163.8 kWh total energy)Sunsynk datasheet, p.2, Scalability |
| Continuous power (per unit) | 5–10 kWEVO 10-5-H: 5 kW · EVO 10-8-H: 8 kW · EVO 10-10-H: 10 kWFox ESS datasheet, p.2, AC output rated power | 3.6–5 kWECCO 3.6K: 3.6 kW · ECCO 5K: 5 kW (larger ECCO models also available)Sunsynk datasheet, p.2, Rated AC Output and UPS Power |
| Peak power | 10–20 kWBackup (EPS) peak for 10 seconds: 10 / 16 / 20 kVA by modelFox ESS datasheet, p.2, EPS output | 7.2–10 kWcalculatedInverter: 2 × rated power for 10 s, off-grid. The batteries' current limits may allow less.Sunsynk datasheet, p.2, Peak Power (off-grid) |
| Architecture | All-in-one: battery with built-in hybrid inverter (solar connects on the DC side)Fox ESS datasheet, p.1 | 48 V low-voltage battery modules with a Sunsynk ECCO hybrid inverter; the inverter supports DC or AC coupling to existing solarSunsynk datasheet, p.1 |
| Max solar input | 16–20 kWMax PV array: 16 kWp (5 kW model), 20 kWp (8 and 10 kW models)Fox ESS datasheet, p.2, PV input | 6.5–7 kWECCO 5K: 6.5 kW · ECCO 3.6K: 7 kWSunsynk datasheet, p.2, Max. DC Input Power |
| Backup switchover time | 4 msLess than 4 msFox ESS datasheet, p.2, EPS switch time | Not documented |
| Backup needs | Built-in EPS (backup) outputFox ESS datasheet, p.1–2 | Not documented |
| Indoor / outdoor | Indoor and outdoor (IP66)calculatedFox ESS datasheet, p.2 | Not documented |
| Dimensions | 584 × 1009 × 197W × H × DFox ESS datasheet, p.2 | 440 × 620 × 135 per moduleW × H × D, excluding breaker and terminalsSunsynk datasheet, p.2 |
| Weight | 113 kgFox ESS datasheet, p.2 | 50 kgPer module, approximate; ECCO inverter 20.5 kgSunsynk datasheet, p.2 |
| Warranty (UK) | 12 yearsFox ESS warranty, p.2, performance warranty table | 10 yearsBattery cells: 10 years or 6,000 cycles. Battery BMS: 5 yearsSunsynk warranty, p.1, §2 Battery warranty |
| Capacity guaranteed at end of warranty | 70%70% of nominal energyFox ESS warranty, p.2 | Not documented |
| Warranty conditions | Not documented | After year 5, faulty cells are replaced free but labour isn't covered. Must be bought from Sunsynk or an authorised reseller, installed in a covered country (the UK is included) and cycled no more than 700 times a year. No capacity-retention figure is given.Sunsynk warranty, p.1, §2, §4 and §5 |
How long each runs your home in a power cut
Every setup we list for both, from a full battery with no solar. Appliance figures are typical estimates; use the calculator below with your own.
| Setup | Usable | Continuous | Essentials (fridge-freezer, lights, Wi-Fi, TV, charging) | Essentials + air-source heat pump (winter) |
|---|---|---|---|---|
| Fox ESS EVO 10-5-H (5 kW) | 9.73 kWh | 5 kW | 2 days 11 hours | 5.6 hours |
| Fox ESS EVO 10-8-H (8 kW) | 9.73 kWh | 8 kW | 2 days 11 hours | 5.6 hours |
| Fox ESS EVO 10-10-H (10 kW) | 9.73 kWh | 10 kW | 2 days 11 hours | 5.6 hours |
| Sunsynk L5.1 with ECCO inverter · ECCO 3.6 kW + 2 × L5.1 (9.2 kWh) | 9.22 kWh | 3.6 kW | 2 days 8 hours | 5.3 hours |
| Sunsynk L5.1 with ECCO inverter · ECCO 5 kW + 2 × L5.1 (9.2 kWh) | 9.22 kWh | 5 kW | 2 days 8 hours | 5.3 hours |
| Sunsynk L5.1 with ECCO inverter · ECCO 5 kW + 3 × L5.1 (13.8 kWh) | 13.83 kWh | 5 kW | 3 days 12 hours | 7.9 hours |
Try your own appliances
Average draw 156 W from 9.24 kWh available.
Everything on at once: 415 W — within the 5 kW limit
- Starts from a full battery with 0% held back as reserve.
- 5% extra allowed for wiring and standby losses on top of the manufacturer's usable figure.
- Appliance figures are typical averages; your own may differ. Enter your own wattage for the most accurate result.
- Assumes no solar recharging during the outage.
- EVO 10: Usable capacity is calculated (10.24 kWh × 95% depth of discharge); Fox ESS does not state a usable figure in this datasheet.
- EVO 10: Round-trip efficiency is not stated; the datasheet gives a 96.4% battery-to-AC figure at full load, which is one direction only.
- L5.1 with ECCO inverter: Sunsynk recommends 50 A per module (about 2.5 kW) and allows up to 100 A. With only one or two modules, the full inverter output may not be sustained for long.
- L5.1 with ECCO inverter: The warranty doesn't guarantee a minimum capacity after a set number of years.
- L5.1 with ECCO inverter: Round-trip efficiency isn't stated on the battery datasheet.
- L5.1 with ECCO inverter: Our ECCO inverter datasheet is version 4 (March 2023), the newest we found for the 3.6 kW and 5 kW models.
Questions people ask
Which can run more appliances at once?
Across the setups we list, Fox ESS EVO 10 delivers 5–10 kW continuously and Sunsynk L5.1 with ECCO inverter delivers 3.6–5 kW. These are the maximums for each setup; installers can set some systems lower. Continuous power limits how many appliances can run at the same time; capacity decides how long they run.
Which has the better warranty?
Fox ESS EVO 10: 12 years, 70% capacity guaranteed at the end. Sunsynk L5.1 with ECCO inverter: 10 years, no capacity figure stated. Conditions differ, so check the warranty rows in the table above.
Do Fox ESS EVO 10 and Sunsynk L5.1 with ECCO inverter work with Intelligent Octopus Flux?
Fox ESS EVO 10: Sold by Octopus for this tariff; not on its FAQ list. Sunsynk L5.1 with ECCO inverter: Not on Octopus's list. Octopus lists the battery brands it can control in its Intelligent Flux FAQ; see our Intelligent Octopus Flux page for details.
Other comparisons
Sources
- EVO 10 Datasheet (UK) V1.0 — Fox ESS, V1.0. Retrieved 26 Sept 2026.
- Fox ESS Battery Warranty Policy (UK) Version 4.5 — Fox ESS, 4.5. Retrieved 26 Sept 2026.
- SUNSYNK-L5.1 datasheet — Sunsynk, v.6 (28/06/24). Retrieved 26 Sept 2026.
- ECCO Hybrid Inverter SUN-3.6/5/6/7.6/8K-SG05LP1-EU datasheet — Sunsynk, v.4 (29/03/23). Retrieved 26 Sept 2026.
- Manufacturer's Warranty — Warranty Agreement Terms and Conditions — Sunsynk. Retrieved 26 Sept 2026.
- Solar & Battery Options (Octopus install packages) — Octopus Energy, Prices based on April 2026. Retrieved 26 Sept 2026.
Spotted an error? See how we check data. Always confirm your final design with an MCS-certified installer.