Incorrect SoC reporting for Solarwatt Vision Three Inverter (technically using the "FoxESS H3 smart" template) house battery

[chrisbeu]

Describe the bug

Problem
The State of Charge (SoC) of my house battery (Solarwatt Vision, technically equivalent to FoxESS H3 Smart) is reported incorrectly in evcc. The values shown in the UI/logs do not match the actual SoC from the inverter.
The evcc value is typically between 2% and >8% too high. The lower the SoC gets - the bigger is the delta.

Environment

• evcc version: 0.211.0
• Inverter: Solarwatt Vision (technically identical to FoxESS H3 Smart) - using the template of FoxESS H3 smart
• Running as Home Assistant OS Add-on

Expected behavior
evcc should correctly display the SoC as reported by the inverter.

Actual behavior
SoC values are inconsistent/incorrect compared to the inverter’s native interface.

Steps to reproduce

1. Configure Solarwatt Vision / FoxESS H3 Smart inverter in evcc.yaml
2. Start evcc
3. Observe SoC values in UI/logs

Additional context
Please advise if this is a known limitation of the FoxESS integration or if adjustments are needed in the template.

I could NOT check it with the nighty version yet.
I'm using Home Asistant with HAOS on a RASPI-5.

Steps to reproduce

Steps to reproduce

1. Configure Solarwatt Vision / FoxESS H3 Smart inverter in evcc.yaml
2. Start evcc
3. Observe SoC values in UI/logs

Configuration details

## minimal configuration 

site:
  title: Home # display name for UI
  meters:
    grid: my_grid
    pv:
      - my_pv
    battery:
      - my_battery

# meter definitions
meters:

### GRID
  - name: my_grid
    type: template
    template: fox-ess-h3-smart
    usage: grid
    # Modbus TCP
    modbus: tcpip
    id: 247
    host: 192.168.100.zzz  # Hostname hier vom Modbus-Proxy
    port: 502 # Port

### PV
  - name: my_pv
    type: template
    template: fox-ess-h3-smart
    usage: pv
    # Modbus TCP
    modbus: tcpip
    id: 247
    host: 192.168.100.zzz  # Hostname hier vom Modbus-Proxy
    port: 502 # Port
    maxacpower: 15000 # Maximale AC Leistung des Hybrid-Wechselrichters (W), optional

### BATTERY
### aLter bisherigen Block für Battery ist nun wieder aktiv, ohne KOrrektur des SoC 😮🙈 ###
  - name: my_battery
    type: template
    template: fox-ess-h3-smart
    usage: battery
    # Modbus TCP
    modbus: tcpip
    id: 247
    host: 192.168.100.zzz  # Hostname hier vom Modbus-Proxy
    port: 502 # Port
    capacity: 10.4 # Akkukapazität (kWh), optional
    minsoc: 10 # Minimaler Ladestand (%), Untere Grenze beim Entladen der Batterie im normalen Betrieb (optional)
    maxsoc: 100 # Maximaler Ladestand (%), Oberes Limit beim Laden der Batterie aus dem Netz (optional)


### Loadpoint definieren, hier als Heizstab ♨️ ###
loadpoints:
  - title: Heizstab
    charger: my_heater # charger

### Charger Definition###
# see https://docs.evcc.io/docs/devices/chargers
chargers:
  - name: my_heater
    type: template
    template: shelly
    host: 192.168.100.xxx
    standbypower: -6000 # Watt
    integrateddevice: # Integriertes Gerät, Fest angeschlossenes Gerät. Keine Ladevorgänge (optional)
    heating: # Wärmeerzeuger, Zeigt °C anstatt % an (optional)
    icon: heater # Icon, Wird in der Benutzeroberfläche angezeigt [car, bike, bus, moped, motorcycle, rocket, scooter, taxi, tractor, rickshaw, shuttle, van, airpurifier, battery, bulb, climate, coffeemaker, compute, cooking, cooler, desktop, device, dishwasher, dryer, floorlamp, generic, heater, heatexchange, heatpump, kettle, laundry, laundry2, machine, meter, microwave, pump, smartconsumer, tool, waterheater] (optional)    


### Stromtarif Netzbezug über Tibber ###
### Einspeisevergütung 6.88ct, nur bei pos. Börsenpreis ###
### Forecast.Solar Einbindung ###
tariffs:
  currency: EUR
  grid:
    type: tibber
    token: <...myToken...>
    
  feedin:
    type: template
    template: energy-charts-api
    bzn: DE-LU
    formula: factor := 1.0; if price < 0 { factor = 0.0 }; factor * 0.0688    

  solar:
    - type: template
      template: forecast-solar
      lat: 49.xxx # Breitengrad
      lon: 12.yyy # Längengrad
      dec: 42 # Neigung, 0 = horizontal, 90 = vertikal
      kwp: 16.2 # Maximale Generatorleistung (kWp)
      az: 9 # Azimut, -180 = Norden, -90 = Osten, 0 = Süden, 90 = Westen, 180 = Norden
      # horizon: 0,0,15,30,45,60,60,60,45,30,15,0 # Horizont, Simuliert Verschattung durch Gelände, [mehr Informationen](https://doc.forecast.solar/horizon) (optional)
      # apikey: # API Key, optional
      interval: 1h # Intervall, optional

Log details

The delta can be seen only when manually comparing the display of inverter to the evcc SoC value.

What type of operating system or environment does evcc run on?

Docker container

External automation

• I have made sure that no external automation like HomeAssistant or Node-RED is active or accessing any of the mentioned devices when this issue occurs.

Nightly build

• I have verified that the issue is reproducible with the latest nightly build

Version

0.211.0

[andig]

The evcc value is typically between 2% and >8% too high. The lower the SoC gets - the bigger is the delta.

It's the value we'r reading. If this needs be post-processed somebody will need to figure out how. That said- nothing we can change without further insights, moving to discussions.

[chrisbeu]

Does anybody have a solution for my issue with incorrect SoC of house battery?
Currently I cannot (yet?) use "scale:" or "offset:" as these features are seemingly not foreseen in the evcc setup.
Is it worth waiting for such features - to be able to correct the read-in-values?
Otherwise evcc is not calculating correctly for charging / discharging the house battery etc...
Thanks for all related hints or help!