battery_plus not created when source entity's registry unit_of_measurement is null at startup (deep-sleep devices)

[bitzer-git]

Checklist

• I have restarted Home Assistant after the HACS or manual install.
• I have read the FAQ's.
• I have enabled debug logging for my installation.
• I have filled out the issue template to the best of my ability.
• This issue only contains 1 issue (if you have multiple issues, open one issue for each issue).
• This issue is not a duplicate issue of any previous issues..

Battery Notes Version

3.6.3

Describe the issue

For an entity-associated battery note on a Shelly Gen1 (H&T, SHHT-1) battery sensor, the battery_plus sensor is unreliably created depending on the state of the entity registry's unit_of_measurement field at Home Assistant startup — not the entity's live state.

Debug log at the time of failure:

sensor.shellyht_15_battery is not a battery entity device_class: battery unit_of_measurement: None
At the same moment, Developer Tools > States confirmed the entity's live attributes were:

state_class: measurement
unit_of_measurement: '%'
device_class: battery

I traced this to the entity registry (core.entity_registry) itself: unit_of_measurement for this entity flips between "%" and null across restarts (confirmed via registry snapshots with timestamps), apparently because this Gen1 (block-protocol) Shelly sensor reports its unit dynamically based on live device data rather than as a fixed value, and the underlying deep-sleep device hasn't reported yet at the exact moment the Shelly platform re-registers the entity on startup.

Manually patching unit_of_measurement to "%" in core.entity_registry and restarting Home Assistant reliably produces a working battery_plus — for exactly one session. Critically, once Battery Notes has determined the entity is invalid, this decision is never re-evaluated: even after confirming a valid live value and manually calling homeassistant.reload_config_entry (for the source entity) and reloading the Battery Notes integration itself, battery_plus remains missing until a fresh process restart with the registry field already correct (by patching).

This suggests two compounding issues:

1. The "is this a battery entity" check should evaluate the live state's attributes (hass.states.get(...).attributes) rather than (or in addition to) the entity registry's unit_of_measurement field, which can be stale/transiently null for dynamically-reporting sensors on deep-sleep devices.
2. The coordinator should re-evaluate entity validity on subsequent refreshes/reloads rather than permanently caching a negative determination for the lifetime of the process.

This may share a root cause with #5077 (battery percent does not persist when battery device goes to sleep) — both issues involve Battery Notes not handling the transient unavailable/missing-attribute state of sleep-cycling battery devices robustly. In #5077 an already-created battery_plus loses its last known value; in this issue, battery_plus is never created in the first place because the one-time validity check happens to run while the registry snapshot is momentarily invalid. A fix that makes Battery Notes tolerant of transient unavailability (e.g. falling back to the last known good value/attributes, or re-evaluating validity on subsequent coordinator refreshes) would likely resolve both.

Reproduction steps

1. Add a Shelly Gen1 H&T (deep-sleep battery sensor with dynamically-reported unit) to HA.
2. Add a Battery Notes entity-association note for its battery sensor.
3. Restart Home Assistant while the device hasn't reported yet in this boot cycle.
4. Observe: battery_plus is not created; debug log shows the entity rejected with unit_of_measurement: None, even though Developer Tools > States (once the device wakes) shows the correct attributes.
5. Waking the device and reloading (both the source integration and Battery Notes) afterward does not create battery_plus — only a full process restart with the registry field already correct works.

System Health details

Version core-2026.8.0
Installation type Home Assistant Container
Development false
Supervisor false
Docker true
Container architecture aarch64
User root
Virtual environment false
Python version 3.14.6
Operating system family Linux
Operating system version 6.12.87+rpt-rpi-2712
CPU architecture aarch64
Timezone Europe/Berlin
Configuration directory /config

Debug logs

2026-09-02 22:54:42.261 DEBUG (MainThread) [custom_components.battery_notes.coordinator] sensor.shellyht_15_battery is not a battery entity device_class: battery unit_of_measurement: None

Diagnostics dump

No response

[andrew-codechimp]

Thanks for the detailed diagnosis on this, Shelly Gen1's are a special case that have been problematic for a long time, this may go some way to explaining this.
#5077 is having an enhancement to cover this which I'm actively working on, where a setting will allow you to ignore unavailable states for sleepy devices, but this won't solve the null at startup of the unit of measurement, which would require more thought.

@chemelli74 know we've talked about this before and never tracked it down, does this sound right from the Shelly integration perspective and wonder if there's anything you can do on that side? Never seen the entity_registry modified like this.