Battery Degradation & Capacity Loss Calculation
| Condition | Total Capacity | Loss (%) | Capacity Loss (kWh) | Energy at 100% | Loss Calculation | Range | Estimated Charging Time at 150 kW DC Fast Charging |
|---|---|---|---|---|---|---|---|
| New Battery | 60 kWh | 0 | 0 kWh | 60 kWh | — | 450 km | ~24 min |
| 10% Capacity Loss | 54 kWh | 0.1 | 6 kWh | 54 kWh | 60 kWh x 0.10 = 6 kWh | 450 − (450×0.10) = 405 km | 54 / 150 × 60 = ~22 min |
| 20% Capacity Loss | 48 kWh | 0.2 | 12 kWh | 48 kWh | 60 kWh x 0.20 = 12 kWh | 450 − (450×0.20) = 360 km | 48 / 150 × 60 = ~19 min |
📌 This table is based on a vehicle with a 60 kWh battery and a nominal range of 450 km. Calculations assume constant speed and consumption, with range calculated linearly. In real-world use, factors such as weather, driving speed, road grade, tire condition, and system efficiency can cause deviations in range and consumption.
⚡ Charging time calculations indicate theoretical minimum time. In real DC charging scenarios, the Battery Management System (BMS) may gradually reduce charging power based on state of charge (SOC), temperature, and cell health. Additionally, the maximum power supported by the charging station and the vehicle affects the time. Therefore, actual charging times may be longer than calculated.
🔍 🔍 Explanation: Battery Chemistry, BMS, and Degradation Over Time
Charging/discharging cycles, temperature, high charging power, and storage cause battery aging. The internal chemical structure degrades → cells lose energy storage capacity.
It always shows the current maximum capacity. So if there is 10% loss, 100% = 54 kWh; if 20% loss, 100% = 48 kWh. Therefore, even if the display shows 100%, it does not contain as much energy as before (less stored energy).
Charging time decreases slightly because less energy needs to be filled.
A battery is not an electronic circuit; therefore, its internal state cannot be known exactly. Calculations are based on current, voltage, energy, and electron flow entering and leaving the battery. Data such as how many hours the battery has been charged and its age are also evaluated to estimate usage time, and the vehicle display shows energy status as % or range. The Battery Management System (BMS) continuously monitors this electron flow, heat, voltage, and current; it limits the battery against overcharge, over-discharge, and overheating. It also generates estimated battery health (SOH) data from charge-discharge cycles.
electrolyte fluid degrades, gas forms, heat increases, cell swelling occurs, fire risk arises, and battery life is significantly shortened.
reverse reactions occur in the chemical structure, electrodes collapse, the cell dies completely and becomes unrecoverable.
The power displayed at the charging station and the vehicle screen are almost identical (e.g., 11 kW AC, 150 kW DC). However, the actual power entering the battery is 5–12% lower for AC and 3–7% lower for DC due to cable and connector losses. The BMS always considers this small difference and protects the battery from over or under charging.
It corrects uncertainties arising from chemical changes in the battery and imbalances between cells, ensuring that the vehicle display shows accurate energy status and battery health. During normal charging, the energy in and out may not be perfectly accurate due to measurement errors, aging, and cable/connector losses; calibration allows the BMS to see the true capacity and SOH.
The first year loss is rapid due to "chemical settling and cell balancing"; after that, the battery stabilizes and loss slows down (around 95%→92%). In the first few charge-discharge cycles, the SEI (Solid Electrolyte Interphase) layer forms; this layer consumes energy chemically. The battery is new, electrode surfaces and electrolyte are not fully stable. Small imbalances and resistance differences between cells also settle. Hence the rapid initial drop.
The SEI layer has settled, chemical structures are stable, cells are balanced. Under the same usage, charge-discharge cycles cause less loss. Result: Annual capacity loss is lower and non-linear, progressing slowly.