A few days after multiple Nikola electric semi-trucks were engulfed in fire in Phoenix, new information revealed that the trucks’ battery modules had defects. The company suspected foul play, but a recent investigation reveals other possible causes.

The Phoenix fire department responded to the incident, and its Hazardous Materials crew rushed to the spot to douse the flames. A new report reveals that engineers detected corrosion in the cells and that the cells would self-discharge, as per internal documents obtained by Electrek.


Nikola Corporation agreed to acquire battery supplier Romeo Power last year for $144 million. Romeo specializes in the design and manufacturing of lithium-ion batteries for commercial vehicle applications, and the transaction is said to save Nikola $350 million annually on battery-related costs.

The team investigating the matter found that several modules faced the same cell corrosion issue. They traced the issue to laser welding, which punctured battery cells in the modules. The cells were corroding within just two test cycles, potentially generating excess heat and increasing the resistance at the joint.

Romeo produces the Hermes and Legion battery modules for the Nikola Tre Class 8 semi truck. It's the latter that made it into the Tre, Nikola told Electrek. As per Electrek's sources, both modules seemed to have a cell puncture issue. 

Although, Nikola told InsideEVs that after the weld issues were identified at Romeo's end-of-line process, a quarantine process was implemented for the inspection of the modules. Packs with weld issues did not make it to the production semi trucks, the company said in a statement.

Gallery: Nikola Tre BEV

A Nikola spokesperson also added that "Legion and Hermes modules use two different cell manufacturers which have unique cell dimensions, height offsets, locations, laser parameters, and ultimately new welding patterns." 

The company said that both the Nikola engineering team and a third-party team have initiated investigations to determine the root cause of the fires, and it will take several weeks for the results to come out.

The Iveco-based Nikola Tre semi truck, made in Coolidge, Arizona, gets an estimated range of 330 miles from a massive 733-kilowatt-hour battery pack. It can charge to 80 percent in just 90 minutes at a rate of 350 kilowatts.

The company halted production of this model last month due to inventory pile-up and disappointing sales. It manufactured 63 units of the BEV in Q1 2023, while the order backlog for the FCEV is 140 units. Its losses have reached almost $170 million, and the fire incident is unlikely to make things any better.

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