Add rate-map battery model and examples

[karakayahuseyin]

Summary

• Add fixed-voltage and rate-map battery model APIs
• Integrate rate-map battery voltage/current behavior into the propulsion solver
• Add example Li-ion cell dataset and battery mission examples
• Reorganize propulsion model dataclasses and runnable examples
• Refresh README/docs visuals and improve MkDocs structure

Validation

• python -m pytest -q → 45 passed
• mkdocs build --strict → passed
• Ran example scripts directly:
  • examples/rate_map_battery_point_states.py
  • examples/rate_map_battery_mission.py
  • examples/calibrate_system_resistance.py
  • examples/select_motor_from_database.py
  • examples/openmdao_hover_optimization.py

Notes

• The included battery dataset is synthetic example data for tests and examples.
• BatterySpec remains as a compatibility alias for FixedVoltageBattery.

Closes #3

[Copilot]

Pull request overview

This PR introduces a lightweight, manufacturer-data-driven battery modeling layer (fixed-voltage and rate-map) and wires it into the propulsion operating-point solver so battery voltage/current outputs reflect the active battery model and state of charge.

Changes:

• Added pythrust.battery models (FixedVoltageBattery, RateMapBattery) plus BatteryState/BatteryPoint, including JSON dataset loading and mission stepping utilities.
• Integrated dynamic battery voltage behavior into PropulsionSolver, expanded OperatingPoint to include battery voltage/current/C-rate/efficiency, and updated OpenMDAO wrapper outputs.
• Added battery-focused tests, examples, and expanded documentation/MkDocs nav to cover the new battery model and refreshed visuals.

Reviewed changes

Copilot reviewed 37 out of 43 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/test_solver.py	Adds solver assertions + new tests for rate-map battery integration behavior.
tests/test_models.py	Updates imports to new dataclass module structure; extends OperatingPoint test fields.
tests/test_battery.py	New unit tests for fixed-voltage aliasing, rate-map point evaluation, stepping, and JSON loading.
scripts/generate_readme_plots.py	Refreshes README plot generation and adds a rate-map mission plot.
README.md	Switches images to repo-relative paths and updates “Feature Visuals” section labeling.
pythrust/propulsion/solver.py	Integrates battery state/point evaluation into the RPM root solve and exposes battery outputs on OperatingPoint.
pythrust/propulsion/models/system.py	New SystemSpec module as part of dataclass reorganization.
pythrust/propulsion/models/propeller.py	New PropellerSpec module as part of dataclass reorganization.
pythrust/propulsion/models/operating_point.py	New OperatingPoint module with added battery output fields.
pythrust/propulsion/models/motor.py	New MotorSpec module as part of dataclass reorganization.
pythrust/propulsion/models/battery.py	Adds compatibility alias BatterySpec = FixedVoltageBattery.
pythrust/propulsion/models/init.py	Re-exports reorganized propulsion dataclasses.
pythrust/propulsion/models.py	Removes monolithic models module in favor of the models/ package.
pythrust/openmdao/components.py	Updates OpenMDAO output to use op.battery_current_a directly.
pythrust/battery/state.py	Introduces BatteryState and BatteryPoint dataclasses.
pythrust/battery/rate_map.py	Adds equivalent-circuit rate-map battery model + JSON loader + stepping utilities.
pythrust/battery/fixed.py	Adds fixed-voltage battery model replacing the historical BatterySpec.
pythrust/battery/init.py	Exposes public battery API surface.
mkdocs.yml	Enables Markdown extensions needed for new docs layout and adds battery docs to nav.
examples/simulate_pybamm_mission.py	Removes PyBaMM-based example script.
examples/select_motor.py	Replaced by the renamed/updated motor selection example.
examples/select_motor_from_database.py	New updated motor selection example using OpenMDAO + database search.
examples/rate_map_battery_point_states.py	New example showing point-state queries on the rate-map battery model.
examples/rate_map_battery_mission.py	New example coupling RateMapBattery to PropulsionSolver over mission segments.
examples/optimize_and_plot_propulsion.py	Replaced by the updated OpenMDAO hover optimization example.
examples/openmdao_hover_optimization.py	New/updated OpenMDAO optimization + sweep example with refreshed plotting.
examples/calibrate_system_resistance.py	Updates calibration example to use FixedVoltageBattery and improves CLI instructions/output.
docs/usage.md	Updates solver usage docs to include battery models/state + new fields + mermaid diagram.
docs/theory.md	Extends theory to include battery model equations and updated coupled equilibrium expression.
docs/motor_calibration.md	Updates battery import/usage for calibration workflow.
docs/index.md	Refreshes landing page structure and feature visuals including battery capability.
docs/getting_started.md	Updates getting started snippets and example commands to new scripts/battery API.
docs/examples.md	Reorganizes examples page and documents the new battery examples.
docs/development.md	Updates development guide example commands and plot regeneration steps.
docs/battery_model.md	New detailed battery model documentation (fixed-voltage + rate-map + dataset format).
docs/api_reference.md	Adds battery model API reference details and documents new OperatingPoint fields.
data/batteries/example_liion_cell.json	Adds synthetic Li-ion cell dataset used by tests and examples.

Comments suppressed due to low confidence (1)

pythrust/propulsion/solver.py:263

• The infeasibility checks overwrite reason as they run, so a later check (e.g., battery infeasible / invalid efficiency) can mask an earlier, more direct failure like current_limit. This makes infeasible_reason non-deterministic with respect to severity/priority and can hide the actual first constraint violated.

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