Nikola Corp. says one of its battery-electric big rigs experienced a “thermal incident” Friday during a test on the cause of recent fires that prompted a recall.

The pre-production truck was undergoing “battery fire investigation and testing” at a facility near its Phoenix, Arizona, headquarters when it caught fire, Nikola said in an email. No one was injured and that the truck was outside when the fire happened.

The event comes days after another truck’s battery pack caught fire at a customer facility. 

A handful of Nikola’s trucks first caught fire in June after a thermal incident in one of the battery packs. The company ultimately identified a single component that it believes to be the cause of the fires, and it issued a recall and stop sale order in August.