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Nissan Leaf Battery Repair Restores Full Power

A high-voltage battery warning can be a worrying sight for any electric vehicle (EV) owner... especially when the car also loses power.

We recently had a 2019 Nissan Leaf arrived at Okee with a battery warning and severely restricted performance, which is commonly known as ‘Turtle Mode’. Our investigation identified a fault within the battery pack, which we managed to repair without replacing the entire battery.

A battery health reading wasn’t the whole story...

The customer told us they had previously visited a dealership and had been advised that a battery replacement would not be covered under warranty. The battery’s reported state of health was 87%. Our own assessment confirmed the same state-of-health (SOH) reading. However, that figure did not tell the whole story... further investigation revealed a voltage imbalance within the battery pack.

The diagnostic readings showed that the section identified as cell 45 was approximately 400 millivolts below the others. This gave us a specific area to investigate rather than treating the whole battery as faulty.

Tracing the fault inside the battery pack

After making the high-voltage system safe to work on, we removed the battery pack from the vehicle and opened it for further testing.

The diagnostic results led us to module 8. When we compared the larger modules, three measured approximately 36.4 volts, while the suspect module measured 35.95 volts.

Further testing within that module revealed the difference... the other individual cell readings were around 4.1 volts, but one measured just 3.65 volts.

These measurements allowed us to pinpoint the faulty part of the pack and carry out a targeted repair.

Replacing the faulty module, not the whole battery

In this case, a complete replacement battery pack was not necessary.

We removed the faulty module, installed its replacement and balanced the battery pack before reassembling it and refitting it to the car.

By repairing the affected part of the battery, we avoided the expense of replacing the complete high-voltage pack.

Back on the road with full power

With the repair complete, we carried out a further battery health check and road-tested the Nissan Leaf.

The car drove normally, full power was restored and the Turtle Mode warning was no longer present.

For this customer, identifying the fault within the pack made the difference between a targeted repair and replacing the entire battery.

Electric vehicle battery diagnostics at Okee

This repair highlights the value of looking beyond a single battery health figure. Although this Leaf reported 87% state of health, our investigation uncovered a fault that needed further testing to identify.

At Okee, we take a methodical approach to electric and hybrid vehicle faults, investigating the cause and explaining the repair options available.

If your electric vehicle is showing a battery warning or suffering from reduced performance, contact Okee to book a diagnostic assessment.