Units convention¶

Internal units, everywhere, after data ingestion:

Quantity	Unit
time	seconds
temperature	K
SoC / DoD / SoH / loss	fraction (0–1)
rate	C-rate

Conversion happens only in two places:

on the way in — esf.io: SampleData.add_data takes time_unit= / temperature_unit=, and the selectors re-unit to the internal convention; OperationalData.from_field_dataframe converts a raw field trace.
on the way out — plotting and reporting.

Reference values such as the calendar-time reference (x_ref = 86 400 s = 1 day) are model parameters, not hidden unit changes.

All pint quantities must come from the single shared registry:

from esf.settings.units import ureg, Q_

Temperature is kelvin, always

The exponential temperature stress model is not invariant under a unit change — its x_ref / x factor differs between a degC and a K parameterization. Mixing the paper's kelvin-parameterized k_temperature constants with a degC reference gives wrong stress factors. Keep temperatures in kelvin.