EP5 ↔ EP6 Plus and EP11 ↔ EP12 Plus (Heating & Non-Heating Versions)
To support battery capacity upgrades over time, Fox ESS has validated cross-generation compatibility between selected EP battery models. This allows customers to expand storage using newer battery variants without impacting system performance.
Note: up to 4 battery modules can be installed in parallel via the Fox ESS EP Junction Box.
Supported Expansion Pairings
The following combinations are fully supported:
Small format batteries
- EP5 ↔ EP6 Plus
- EP5-(w) ↔ EP6 Plus-(w) (heated versions)
- EP5-(w) ↔ EP6 Plus (non-heated)
- Heating hardware remains present, but the warming function becomes inactive across the system.
Large format batteries
- EP11 ↔ EP12 Plus
- EP11-(w) ↔ EP12 Plus-(w) (heated versions)
- EP11-(w) ↔ EP12 Plus (non-heated)
- Heating hardware remains present, but the warming function becomes inactive across the system.
Heating Function Clarification
Where a heated battery model is paired with a non-heated model, the system will continue to operate normally, however:
- The battery warming feature is disabled system-wide
- There is no impact on electrical performance, safety, or charge/discharge capability
- The limitation applies only to thermal pre-conditioning functionality
Important Compatibility Limitation
EP5 / EP6 Plus batteries cannot be mixed with EP11 / EP12 Plus batteries.
These two battery size classes use different electrical and system architectures and must not be installed together in the same installation.
Aesthetic & Mechanical Notes
EP and EP Plus models feature different external designs and casing styles, meaning:
- Visual differences may be noticeable when mixed in a stack
- There is no functional, performance, or safety impact
- Installers should consider appearance expectations when planning expansions
Summary for Installers & Customers
| Scenario | Supported | Notes |
|---|---|---|
| EP5 + EP6 Plus | ✅ Yes | Fully compatible |
| EP11 + EP12 Plus | ✅ Yes | Fully compatible |
| Heated + Heated | ✅ Yes | Full warming functionality retained |
| Heated + Non-Heated | ✅ Yes | Warming disabled |
| EP5/EP6 with EP11/EP12 | ❌ No | Not permitted |
Official Validation
Fox ESS has completed testing and validation to confirm these compatibility rules.
