West Sussex Fire and Rescue Service has ruled out Tesla cars, chargers or batteries as causes of the blaze at a Tesla dealership in County Oak Way, which was judged to have been started accidentally.
A fire service spokesman said the fire is thought to have started in the storeroom.
Firefighters were called to the incident at 10.28am after receiving several 999 calls, amid reports of several small explosions.
At its height, eight fire engines, including crews from Surrey Fire and Rescue Service, were battling the fire.
Adrian Murphy, WSFRS area manager for response, said: “Our fire crews were on the scene within four minutes and found a rapidly spreading fire.
“With the assistance of Tesla staff on the scene and later crews from Surrey, the fire was soon brought under control and at around midday the incident was scaled back.”
Crews managed to contain the damage of the building to 25% with a further 25% being damaged by heat and smoke.