EV Battery Capacity Degradation,
Charging Handshake Failure,
HV (High Voltage) Isolation Fault,
BMS (Battery Management System) Error,
On-Board Charger (OBC) Malfunction,
Diagnostic Overview
The System: EV battery health and charging involve three main stages: the charging station (EVSE), the On-Board Charger (OBC) which converts AC to DC, and the Battery Management System (BMS) which protects the cells.
The Problem: Problems usually fall into two categories: Physical Connectivity (won't start charging) or Chemical Health (driving range has dropped significantly).
Common Failure Points
Connector Pin Arcing: If the charging handle is pulled out frequently while active, or if dirt enters the port, the pins can develop "pitting." This creates resistance, causing the port to overheat and the car to throttle the charging speed to a crawl.
On-Board Charger (OBC) Failure: If your car charges fine on a DC Fast Charger (Tesla Supercharger/Electrify America) but fails at home on a Level 2 plug, your internal OBC is likely faulty.
12V Accessory Battery: Ironically, many "High Voltage" battery errors are caused by a weak 12V lead-acid battery. If the 12V system is low, it cannot "close the contactors" (the heavy-duty switches) to allow the big battery to charge.
Thermal Management (Coolant Leak): Batteries must stay between 20°C and 45°C to charge at full speed. If the cooling pump fails or the coolant level is low, the BMS will block fast charging to prevent a fire.
Understanding Battery Degradation
| Phenomenon | Cause | Is it "Normal"? |
| Calendar Aging | Natural chemical breakdown over time. | Yes (approx. 1–2% per year). |
| Cycle Aging | High mileage and frequent 0% to 100% cycles. | Yes. |
| Rapid Drop | A "bad cell" or unbalanced module in the pack. | No. This is a warranty issue. |
| Winter Range Loss | Lithium ions move slower in the cold; heater use. | Yes (temp recovery occurs in spring). |
Troubleshooting Steps
The "Lid" Check: Ensure the charging port door is fully engaging its sensor. If the car doesn't "see" the door is open/closed, it will lock out the charging sequence.
Inspect the Pins: Look inside the car's charging port for "green" oxidation or black scorch marks. Use compressed air to blow out any debris.
Check BMS State of Health (SoH): Most EVs have a hidden menu or a smartphone app (like OBDAmigo or ScanMyTesla) that reveals the State of Health. If the SoH is below 70–80% within the warranty period (usually 8 years/100k miles), you may be eligible for a free replacement.
Reset the Charger: If charging at home, flip the breaker for your charger off for 30 seconds. A "logic hang" in the wall box often looks like a car failure.
Critical Tip: The 80% Rule
To minimize degradation, avoid leaving your car at 100% or 0% state of charge for more than a few hours. Keeping the battery between 20% and 80% can double the lifespan of the cells.
Would you like me to look up the specific "Battery Warranty" terms and the "Battery Health" hidden menu access for your vehicle?
Diagnosing EV Charging Issues and Battery Health
This video explains how to use an OBD2 adapter to check individual cell voltages and how to determine if a charging fault is coming from the car or the charging station.
