“It exploded, just like a flare, and filled the car with toxic smoke," the 74-year-old told The Local.
"I couldn't see anything and knocked my tooth out while throwing the damn thing out the window!”
Wallgren has spent his life trying to make products safer and was shocked that the iPhone did not have a warning explaining the danger of removing the battery.
“It was scary but it would've been worse if it had happened in my house. The whole place could have burnt down,” he said.
Meanwhile, Nora Ay of Siba, an electronics retailer that sells iPhones in Sweden, told the local Göteborgs-Posten (GP) newspaper that she has never heard of an iPhone catching fire, adding that the product's handbook explains that owners should never replace batteries themselves.
Wallgren, however, explained that he wants the public to know about his accident as he believes worse problems may occur for others if Apple doesn't enclose a warning text in the phone itself.
“A product should work and be safe, and if it doesn't, the company should take responsibility,” he said.
Apart from being told by the store that the phone is irreparable, he has not received any explanations as to why it started to burn and now claims to be very sceptical about iPhones in general.
“No one has explained why this happened. The phone is crap and I'm not going to buy another one,” he told The Local.