Fix incorrect SoC when battery_scaling_auto is enabled

[nickgee31]

Fixed battery degradation auto-scaling so it respects the configured battery_scaling baseline.

Previously, battery_scaling_auto could update soc_max without keeping the effective runtime battery scale consistent. This could make Predbat’s displayed SoC diverge from the real inverter SoC, especially on systems using battery_scaling for DoD correction, such as 0.8.

The change now treats the configured per-inverter battery_scaling value as the upper bound, and only allows auto degradation to reduce from that baseline. For example, battery_scaling: 0.9 can auto-adjust within 0.72-0.9, while battery_scaling: 0.8 can adjust within 0.64-0.8. This preserves manual DoD/SOH correction while still allowing measured battery degradation to be applied consistently to both soc_max and shown SoC.

#3940 - fixes this issue.

[Copilot]

Pull request overview

This PR fixes a battery degradation auto-scaling inconsistency that could cause Predbat’s displayed SoC to drift from the inverter’s real SoC when battery_scaling_auto is enabled alongside a configured battery_scaling baseline (e.g., DoD correction like 0.8). It does this by treating the configured battery_scaling as an upper bound and only allowing auto-scaling to reduce from that baseline.

Changes:

• Introduces a per-inverter baseline (battery_scaling_config) captured from the configured battery_scaling value.
• Updates battery_size_tracking() to clamp auto-scaling to [0.8 * configured_scaling, configured_scaling] and to update self.battery_scaling alongside soc_max.
• Extends the battery sizing tests to validate both soc_max and battery_scaling, including a new case ensuring configured scaling is preserved as an upper bound.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
apps/predbat/inverter.py	Stores configured scaling baseline and clamps battery_scaling_auto relative to it while updating runtime battery_scaling consistently.
apps/predbat/tests/test_find_battery_size.py	Updates expected scaling calculations and adds coverage ensuring auto-scaling respects configured battery_scaling as the cap.