bat-volt-fault on a Fox ESS battery: Battery voltage fault. Check if the battery input voltage is within the normal range
Short answer
On a Fox ESS battery, bat-volt-fault means: Battery voltage fault. Check if the battery input voltage is within the normal range. The battery keeps running with some functions stopped. The wording differs by model range — each is shown below.
Reviewed 24 September 2026 · 2 sources
What it means
On the EVO all-in-one
The manual says: Battery voltage fault. Check if the battery input voltage is within the normal range.
On the H1 G2 single-phase hybrid inverter
The manual says: Battery voltage fault.
Part involved: battery input voltage.
When it shows: Battery voltage out of range.
Likely causes:
- Battery voltage outside inverter's allowed range; battery switched off or tripped.
Is it safe?
On the EVO all-in-one
| Does the battery stop? | Partly |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
The battery keeps running with some functions stopped.
Resetting itself: unknown.
Manual reset: see solution.
On the H1 G2 single-phase hybrid inverter
| Does the battery stop? | Partly |
|---|---|
| Engineer needed? | Yes |
The battery keeps running with some functions stopped.
Resetting itself: unknown.
Manual reset: Check battery input voltage; seek help.
What you can check
On the EVO all-in-one
- Read and note the exact code or light pattern and the time (photo or app screenshot). The EVO shows the fault name on its LCD touchscreen (red LED = fault mode).
- Check the battery/inverter AC isolator and the consumer-unit breaker are ON. Do not keep resetting a breaker that trips again straight away.
- Check the monitoring app shows the system online and the home Wi-Fi/router is working.
- The manual's fix ('disconnect PV, grid and battery, then reconnect') includes DC switching inside an all-in-one battery - ask your installer to do it or talk you through the safe sequence.
- Never open the battery, inverter or gateway casing and never touch DC cables, connectors or battery terminals.
- If the code stays or keeps coming back, contact your installer (quote the code) - do not keep power-cycling.
On the H1 G2 single-phase hybrid inverter
- Read the full code and message on the inverter screen or in the FoxCloud app and note the date/time for your installer.
- Check the inverter's AC isolator next to the inverter and the solar/battery breaker in the consumer unit are ON (do not reset a breaker that trips again - call your installer).
What the engineer will check
On the EVO all-in-one
- Measure battery bus voltage; check BMS state codes (BS1-BS6).
Who to ask for: battery storage installer.
Certification: Fox ESS approved installer (Fox ESS warranty excludes repairs by unauthorised persons); MCS battery certification.
On the H1 G2 single-phase hybrid inverter
- Measure battery voltage at inverter terminals; check battery breaker/switch, DC cables and BMS state.
Who to ask for: Battery/hybrid installer trained on the specific battery (manufacturer-approved installer).
Certification: Battery and hybrid-inverter DC work: installer trained/approved by the manufacturer; electrical work under BS 7671 by a competent person.
What you might notice
Sources
- EVO 5 / EVO 10 Series User Manual V1.0.0 (10-500-10451-00) ↗ · V1.0.0 · page 51 · Reviewed 24 September 2026
- H1(G2)/AC1(G2) Series User Manual ↗ · V1.0.8 · page 47 · Reviewed 24 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 24 September 2026