0011 — Stored energy and session energy get their own Home Assistant classes

Status: Accepted Context: Home Assistant validates device_class against state_class and, since 2026.9.0, logs a warning for every entity that gets the pair wrong:

Entity <id> is using state class 'measurement' which is impossible considering device class ('energy') it is using; expected None or one of 'total_increasing', 'total'

Four entities published by this service were affected, all of them through one shared sensor type, ENERGY_MEASUREMENT_WH (energy / measurement / Wh): the three battery capacity fields maximum_energy, available_energy and rated_energy, and the EV charger's session_energy. The two are not the same kind of value, so the shared type had to be split rather than corrected in place.

Decision 1: battery capacities are energy_storage, not energy

Decision: The battery capacity fields use a new ENERGY_STORAGE_WH sensor type — device_class: energy_storage, state_class: measurement, unit Wh.

Context: These fields describe how much energy the battery holds or can hold right now. They rise and fall, they do not accumulate, so measurement is the state class that describes them and it is the one that had to survive. energy_storage is Home Assistant's device class for exactly that, and it accepts measurement and nothing else.

Changing the state class to total_increasing instead was rejected: it would have silenced the warning while telling Home Assistant that a falling battery level is a meter reset.

Consequence: No statistics migration. energy_storage keeps the mean-based statistic these entities already had, so their history stays intact and continues as before.

Decision 2: EV charger session energy is total_increasing

Decision: session_energy reuses the existing ENERGY_WH type — device_class: energy, state_class: total_increasing, unit Wh.

Context: This value really does accumulate over a charging session and drops back to zero when the next one starts. That reset is what total_increasing exists for: Home Assistant treats a drop as the start of a new cycle rather than as negative consumption.

Moving it to energy_storage alongside the battery fields was rejected. It would have matched the old state class and needed no migration, but it would describe a session counter as a storage level and keep it out of the energy dashboard.

Consequence: The long-term statistic for this entity changes from mean/min/max to sum. Home Assistant would raise a repair issue over changed statistics for an entity that already existed under the old class, requiring the old measurement-type statistics to be deleted under Developer Tools → Statistics before the sum statistic starts — but the EV charger integration this entity belongs to has not shipped yet, so no installation carries the old class and the migration step does not apply to anyone.