Signs of a failing EV battery

1. Sudden range loss

A drop of 15% or more within weeks. Genuine degradation does not work this way. Sudden loss almost always means one module has failed and the battery management system is limiting the whole pack to protect it.

2. A wide cell-voltage spread

The definitive indicator, and the reason a proper diagnostic matters. A healthy pack holds all cells within a few tens of millivolts. A spread of 100 mV or more means specific cells are failing, even if total capacity still looks acceptable.

3. Charging that stops early or slows dramatically

Particularly on DC fast charging. If the car used to take 150 kW and now tapers at 50, or stops at 80% and refuses to continue, something in the pack or its thermal management has changed.

4. Power limits under acceleration

A "reduced power" warning, or the car simply feeling flat when it did not before. A pack that cannot deliver current is a pack with a problem.

5. Thermal management running constantly

Cooling that runs when parked in mild weather, or a pump audibly working hard on a cool day, suggests the pack is generating heat it should not be — or that the cooling system itself has failed, which will damage the pack if left.

6. Explicit warnings

High-voltage system faults, "service battery" messages, or a P0A80-family code. These are unambiguous: get it diagnosed.

• Cold weather. Indicated range can fall 20–30% below freezing, because heating the cabin and the pack costs energy and cold cells deliver less. It returns completely in spring.
• The first 3–5% of loss. Nearly every EV loses a few percent in the first 20,000 miles as the pack settles, then the curve flattens hard.
• An optimistic range estimate. The guess-o-meter learns from recent driving. A few motorway trips or a roof box will move it substantially with no change to the battery.
• Slower charging in the cold. Packs must be warmed before they accept high current. Preconditioning on the way to a charger fixes this.
• Higher consumption in winter. Cabin heating is a real, large load. It is not degradation.

Judge your range in mild weather, on a familiar route, over months rather than days.

Several much cheaper problems produce the same symptoms:

• 12 V battery failure ($150–$450) — dramatic electrical symptoms, sometimes a car that will not wake at all.
• Onboard charger fault ($900–$2,500) — AC charging fails while DC still works.
• Charge port damage ($400–$1,200) — intermittent or failed charging, often with visible scorching.
• Coolant pump or heater ($600–$1,900) — charging limits and thermal warnings.
• Contactor or pyro-fuse ($500–$1,500) — the car will not power up; the pack is fine.
• A software issue ($0) — occasionally a BMS calibration problem that a recalibration or update resolves.

1. Record what you are seeing. Dates, range figures, charge percentages, error messages. A pattern is far more useful to a technician than "it feels worse".
2. Try a full-range recalibration. On many EVs, charging to 100% and running down to around 10% once lets the BMS re-learn actual capacity. This alone resolves a surprising number of "sudden" range drops.
3. Check your warranty status. Age, mileage, and the capacity threshold — usually 70%. If you are close to the limit of coverage, act now rather than later.
4. Get a documented state-of-health test ($100–$300). This is the step that converts uncertainty into a number.
5. If a pack is quoted, get a second opinion from a shop that can read cell-level data. Full-pack quotes frequently become module repairs at this stage.