The Fox ESS CQ7 Slave (Part No: FE-CQ7-S) is the battery expansion module for the Fox ESS CQ7 high-voltage storage system, adding a further 7.02kWh of LiFePO₄ (LFP) capacity to any existing CQ7 stack. Unlike the Master module, the Slave contains battery cells only — no system controller — keeping each added module lighter and simpler to install. Slave modules are added one at a time in series with a single CQ7 Master (FE-CQ7-M, sold separately) to scale a stack from 14.04kWh up to a maximum of 98.28kWh.
>95%
Round-Trip Efficiency
Qualified Installation Required
High-voltage battery wiring must be carried out by a qualified, competent electrician in accordance with BS 7671 and Part P of the Building Regulations. Where the installation forms part of an MCS-certified renewable system, work must be completed by an MCS-accredited installer.
Requires a CQ7 Master to Operate
The CQ7 Slave is a battery-only expansion module and cannot function as a standalone system. Every stack must include exactly one CQ7 Master (FE-CQ7-M), sold separately, which provides the system controller, BMU and inverter communication that the whole stack relies on.
Plug-and-Play Capacity Expansion
Each Slave module simply stacks in series on top of the existing tower, adding 7.02kWh of usable LFP capacity per unit with no additional control electronics required. Up to 13 Slave modules can be combined with a single Master, taking total stack capacity as high as 98.28kWh.
Why It Performs
Pure Capacity Expansion
Adds 7.02kWh of LiFePO₄ capacity per module with no duplicate control electronics, keeping incremental expansion cost-efficient as a stack grows.
CAN Communication
Integrates into the stack's CAN bus, reporting cell-level data back to the Master module for accurate state-of-charge and balancing across the full tower.
Scalable Architecture
Up to 13 Slave modules can be installed in series with one Master, allowing installers to size a system precisely to the property's storage requirement.
Integrated Fire Protection
Built with a dedicated fire protection function and multiple electrical protection layers for safe operation in occupied residential settings.
Wide Operating Window
Rated to discharge down to -10°C as standard, with an optional internal warm-up function extending charge and discharge operation down to -25°C.
Outdoor-Rated, Fanless Design
IP65-rated housing with natural convection cooling means no moving parts and no fan noise — suitable for indoor or outdoor floor-standing installation.
Technical Specification
| Specification |
Value |
| Electrical Characteristics |
| Battery Type |
LFP (LiFePO₄) |
| Nominal Capacity (per module) |
7.02kWh |
| Nominal Voltage (per module) |
57.6V |
| Max. Charge/Discharge Current |
80A |
| Recommended Charge/Discharge Current |
50A |
| Peak Discharge Current |
110A (60 sec) |
| Battery Pack Round-Trip Efficiency |
>95% (@25°C, 0.3C) |
| Depth of Discharge |
90% |
| Communication |
CAN |
| Display |
1 x status LED |
| Specification |
Value |
| Operating Conditions |
| Installation Location |
Outdoor / Indoor (floor-standing on stand) |
| Operating Temperature (standard) |
Charge: 0~55°C | Discharge: -10~55°C |
| Operating Temperature (optional warm-up) |
Charge: -25~55°C | Discharge: -25~55°C |
| Storage Temperature |
-10~50°C |
| Cooling Method |
Natural convection |
| Humidity |
5~95% (non-condensing) |
| Max. Operating Altitude |
3,000m |
| Specification |
Value |
| Certification & Protection |
| Fire Protection Function |
Yes, integrated |
| Ingress Protection |
IP65 |
| Safety |
IEC 62619 |
| EMC |
IEC 61000-6-1 / -2 / -3 / -4 |
| Transportation |
UN38.3 |
| Max. Modules in Series |
14 (1 Master + up to 13 Slaves) |
Stack Sizing Reference (1 x Master + Slaves)
| Stack |
Modules |
Capacity |
Operating Voltage |
Stack Dimensions (W x D x H) |
Stack Weight |
| L2 (min. stack) |
1M + 1S |
14.04kWh |
115.2V |
660 x 360 x 420mm |
105.5kg ±5% |
| L3 |
1M + 2S |
21.06kWh |
172.8V |
660 x 360 x 575mm |
156.0kg ±5% |
| L4 |
1M + 3S |
28.08kWh |
230.4V |
660 x 360 x 730mm |
206.5kg ±5% |
| L5 |
1M + 4S |
35.10kWh |
288.0V |
660 x 360 x 885mm |
257.0kg ±5% |
| L6 |
1M + 5S |
42.12kWh |
345.6V |
660 x 360 x 1040mm |
307.5kg ±5% |
| L7 (max. for H1-G2 / K series) |
1M + 6S |
49.14kWh |
403.2V |
660 x 360 x 1195mm |
358.0kg ±5% |
Frequently Asked Questions
Can I install a CQ7 Slave module without a Master?
No. The Slave module contains battery cells only and has no system controller of its own. It must be connected in series with exactly one CQ7 Master (FE-CQ7-M) to form a working stack.
How many Slave modules can I add to one Master?
Up to 13 Slave modules can be added to a single Master, taking total stack capacity to a maximum of 98.28kWh. The practical limit depends on the connected inverter — for example, the H1-G2 and KH/KA series support a maximum of 6 Slaves (7 modules total, 49.14kWh) per stack.
Can I add Slave modules to an existing CQ7 stack later?
Yes — the modular, plug-and-play design is built for this. Additional Slave modules can be stacked in series with the existing Master as storage requirements grow, up to the inverter's supported maximum.
Does the CQ7 Slave need the optional warm-up function for UK installations?
It depends on the installation location. Standard units charge down to 0°C; for unheated outdoor enclosures in colder parts of the UK, the optional warm-up variant (extending charge capability to -25°C) is worth specifying, and should match the Master and any other Slaves in the same stack.
Is the CQ7 Slave suitable for outdoor installation?
Yes — it carries an IP65 ingress protection rating and uses natural convection cooling with no fan, making it suitable for both indoor and outdoor floor-standing installation on a stand.
What is the difference between the CQ7 Slave and CQ7 Master?
The Slave (FE-CQ7-S) is a pure 7.02kWh battery module with no system controller, used to add capacity to an existing Master. The Master (FE-CQ7-M) contains the system controller, BMU and switchgear in addition to its own 7.02kWh battery module, and is required once per stack.
