Available as legacy non-heated EP5 and heated EP5-H variants.
View EP5-H →Fox ESS technical buying guide
Fox EP battery compatibility made simple
Understand which Fox ESS EP5, EP6, EP11 and EP12 batteries can be combined, when heating is affected, why firmware matters and when a Fox HV Junction Box is required.
2 groupssmall and large format batteries
V1.010+firmware for supported mixed-model pairs
4-wayFox HV Junction Box connection
Label firstcheck the exact suffix before ordering
Identify your battery
Start with the exact EP model and suffix
The model is normally shown on the battery label, packaging and in FoxCloud. Do not rely on appearance alone: heated variants and newer replacements can look very similar.
Heated, slimline replacement option within the smaller EP group.
View EP6 →Available as legacy non-heated EP11 and heated EP11-H variants.
View EP11-H →Heated, slimline replacement option within the larger EP group.
View EP12 →What about EP3? EP3 is also part of the Fox high-voltage EP family, but it is not automatically covered by the EP5/EP6 or EP11/EP12 cross-model pairings in this guide. Confirm an EP3 expansion with Fox ESS or our team before ordering.
Compatibility matrix
Which Fox EP batteries can be mixed?
The table is a purchasing guide for the EP5, EP6, EP11 and EP12 families. Final approval still depends on the complete system and current Fox firmware requirements.
| Combination | Status | Important conditions |
|---|---|---|
| EP5 with EP5-H | Compatible | Heating is disabled when heated and non-heated variants are combined. |
| EP5 with EP6 | Conditional | Use firmware V1.010 or newer across the batteries; matching models remains preferable. |
| EP11 with EP11-H | Compatible | Heating is disabled when heated and non-heated variants are combined. |
| EP11 with EP12 | Conditional | Use firmware V1.010 or newer across the batteries; matching models remains preferable. |
| EP5/EP6 with EP11/EP12 | Not compatible | Do not combine the smaller and larger battery groups in one battery system. |
| More than one EP battery | Extra hardware | A Fox HV Junction Box is required for parallel connection; system limits depend on the inverter. |
Heated vs non-heated
Mixed systems lose the heating function
Heated and non-heated versions can be used together within the appropriate compatible EP group, but the heating function is disabled across the mixed system. Electrical storage performance is otherwise unaffected when the combination and configuration are approved.
If the installation location regularly experiences low temperatures, retaining heating may be valuable. In that case, use matching heated batteries rather than mixing variants.
Expansion hardware
When is the Fox HV Junction Box needed?
A single compatible EP battery connects without the parallel Junction Box. Connecting two, three or four EP batteries in parallel requires the Fox HV Junction Box.
Some inverter platforms, including suitable H3 PRO configurations, can support greater totals through multiple battery inputs. Never assume that the maximum number shown for one inverter applies to another model or generation.
View Fox HV Junction BoxNo parallel Junction Box
Fox HV Junction Box required
Model, generation and firmware matter
Product links retained
Shop Fox ESS EP batteries and expansion hardware
Use the guide above before ordering. Product availability and prices are shown on the individual product pages.
HeatedFox EP5-H5.18kWh batteryView product →
HeatedFox EP65.76kWh batteryView product →
HeatedFox EP11-H10.36kWh batteryView product →
HeatedFox EP1211.52kWh batteryView product →
Legacy referenceFox EP55.18kWh non-heatedView product →
Legacy referenceFox EP1110.36kWh non-heatedView product →
Expansion hardwareHV Junction BoxUp to four parallel inputsView product →
Complete rangeAll Fox EP productsView batteries and accessoriesBrowse range →
Before ordering
Send us a label photo and avoid an expensive mistake
Battery returns are awkward and expensive, so we would much rather check the proposed expansion first. Include the five items opposite and we can help identify the sensible route.
- Battery labelClear photograph showing the full model, suffix and serial number
- Inverter labelExact model, generation and rated power
- Current battery countHow many batteries and whether a Junction Box is already fitted
- Firmware informationBattery and inverter firmware if visible in FoxCloud
- Expansion planThe model and quantity you want to add
Common questions
Fox EP compatibility FAQs
Use these answers as an initial check. Firmware releases and manufacturer requirements can change, so verify the complete system before installation.
Can Fox EP5 and EP6 batteries be used together?
Yes, subject to the correct firmware and configuration. Current product guidance requires firmware V1.010 or newer across the batteries. We still recommend matching battery models where practical.
Can Fox EP11 and EP12 batteries be used together?
Yes, subject to the correct firmware and configuration. Current product guidance requires firmware V1.010 or newer across the batteries. Matching models remains preferable where practical.
Can EP5 or EP6 be mixed with EP11 or EP12?
No. The smaller EP5/EP6 group must not be combined with the larger EP11/EP12 group in the same battery system.
Can heated and non-heated batteries be mixed?
Compatible heated and non-heated variants can be combined within the appropriate group, but heating is disabled across a mixed heated and non-heated system.
Is a Junction Box always required?
No. It is not required for a single battery. The Fox HV Junction Box is required when compatible EP batteries are connected in parallel.
How many EP batteries can I connect?
The Junction Box provides up to four parallel battery inputs. Some compatible inverter systems can support higher totals through more than one battery input, but the exact limit depends on the inverter model, generation and system design.
How do I identify the exact battery?
Use the model and serial-number label on the battery. The packaging and FoxCloud may also show the model, but a photograph of the physical label is the most useful starting point.
Sources & scope
Manufacturer resources
Technical details checked on 21 August 2026.
Still unsure which battery to add?
Email a photograph of the existing battery label and inverter label before ordering. We will help check the likely compatibility route and any additional hardware required.