docs/dataset.md

Dataset Documentation

NASA PCoE Li-ion Battery Dataset

Source

• Repository: NASA Prognostics Center of Excellence (PCoE)
• Reference: B. Saha and K. Goebel (2007). Battery Data Set, NASA Prognostics Data Repository, NASA Ames Research Center, Moffett Field, CA
• URL: https://www.nasa.gov/content/prognostics-center-of-excellence-data-set-repository

Cells

• Type: Li-ion 18650
• Nominal capacity: 2.0 Ah
• Count: 30 batteries after cleaning (from original 36)
• Total discharge cycles: 2,678
• Sliding windows generated: 1,734 (window size = 32 cycles)

Temperature Groups (discovered in EDA)

Group	Temperature	# Batteries	# Cycles
1	4°C	3	~200
2	22°C	4	~280
3	24°C	16	~1700
4	43°C	4	~320
5	44°C	3	~180

Note: 5 temperature groups were discovered (not 3 as originally assumed).

End-of-Life Definitions

• 30% capacity fade: 1.4 Ah (default threshold)
• 20% capacity fade: 1.6 Ah (alternative)

Cycle Types

Discharge

Columns: Voltage_measured, Current_measured, Temperature_measured, Current_load, Voltage_load, Time

Charge

Columns: Voltage_measured, Current_measured, Temperature_measured, Current_charge, Voltage_charge, Time

Impedance

Columns: Sense_current (Re + Im), Battery_current (Re + Im), Current_ratio (Re + Im), Battery_impedance (Re + Im)

Metadata Schema (metadata.csv)

• type: cycle type (charge, discharge, impedance)
• start_time: MATLAB datenum
• ambient_temperature: °C
• battery_id: identifier
• test_id: test sequence number
• uid: unique identifier
• filename: path to cycle CSV
• Capacity: measured capacity (Ah)
• Re: electrolyte resistance (Ω)
• Rct: charge transfer resistance (Ω)

Feature Engineering

Per-Cycle Scalar Features (12 dimensions)

1. cycle_number — sequential cycle index
2. ambient_temperature — environment temperature
3. peak_voltage — max voltage in cycle
4. min_voltage — min voltage in cycle
5. voltage_range — peak - min
6. avg_current — mean current magnitude
7. avg_temp — mean cell temperature
8. temp_rise — max - min temperature
9. cycle_duration — total time (s)
10. Re — electrolyte resistance
11. Rct — charge transfer resistance
12. delta_capacity — capacity change from previous cycle

Derived Targets

• SOC: Coulomb counting (integrated current)
• SOH: (Current capacity / Nominal capacity) × 100%
• RUL: Cycles remaining until EOL threshold
• Degradation State: Healthy (≥90%), Moderate (80–90%), Degraded (70–80%), End-of-Life (<70%)