The Fox ESS CQ7 Master (Part No: FE-CQ7-M) is the system controller module that powers every Fox ESS CQ7 high-voltage battery stack. Built around a 7.02kWh LiFePO₄ (LFP) cell module, the Master integrates the Battery Management Unit (BMU), switchgear and CAN communication interface that the whole stack relies on to talk to a compatible Fox ESS hybrid inverter. Every CQ7 system — from the smallest 2-module stack to the largest 14-module tower — requires exactly one CQ7 Master, paired with one or more CQ7 Slave modules (sold separately) to reach the required capacity.
>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.
One Master Per System
Exactly one CQ7 Master is required per CQ7 stack — it cannot be used alone. It must be combined with at least one CQ7 Slave (FE-CQ7-S), sold separately, and a compatible Fox ESS hybrid inverter (H1-G2, KH/KA series, H3 Smart/Plus/Pro). Maximum stack size and module count depend on the inverter model — check compatibility before specifying.
The Brain of the CQ7 Stack
The Master module houses the system controller, BMU and switchgear for the entire stack, while each Slave module adds pure battery capacity. This split keeps the Slave units lighter and simpler, while the Master coordinates charge/discharge balancing, fault protection and inverter communication across up to 14 modules in series (98.28kWh total capacity).
Why It Performs
Integrated System Controller
Houses the BMU, switchgear and monitoring interface for the complete CQ7 stack, coordinating every connected Slave module from a single point of control.
CAN Communication
Communicates directly with compatible Fox ESS hybrid inverters over CAN bus, enabling accurate state-of-charge reporting and coordinated charge/discharge scheduling.
Scalable to 14 Modules
Supports up to 13 Slave modules in series with the single Master, scaling a stack from 14.04kWh to a maximum of 98.28kWh depending on the connected inverter.
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 |
6 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 buy the CQ7 Master on its own and run it without a Slave module?
No. The Master module provides system control but very little usable capacity on its own. Fox ESS specifies a minimum stack of one Master plus one Slave (FE-CQ7-S) for a working battery system.
How many Slave modules can one Master support?
Up to 13 CQ7 Slave modules can be added in series with a single Master, giving a maximum single-stack capacity of 98.28kWh. The practical maximum depends on the connected inverter — for example, the H1-G2 and KH/KA series support up to 7 modules (49.14kWh) per stack.
Which Fox ESS inverters is the CQ7 Master compatible with?
The CQ7 stack is designed to pair with Fox ESS hybrid inverters that support CAN-based high-voltage battery communication, including the H1-G2 / AC1-G2, KH/KA series, and H3 Smart, H3 Plus and H3 Pro ranges. Always confirm the specific inverter model's maximum stack size before ordering.
Does the CQ7 Master 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.
Is the CQ7 Master 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 Master and CQ7 Slave?
The Master (FE-CQ7-M) contains the system controller, BMU and switchgear in addition to its 7.02kWh battery module, and is required once per stack. The Slave (FE-CQ7-S) is a pure 7.02kWh battery module with no system controller, used to add capacity to an existing Master.
