Amazon sold an external iPhone charger to a customer that ended up backfiring.

A Philadelphia man claims his fiancee bought him an EasyAcc external battery pack charger from Amazon.com, and after having it for about 9 months ... it blew up last year and caught fire in his pants pocket. Apparently there's security footage of the explosion.

The guy was using the charger as intended when it spontaneously ignited and exploded, causing severe injuries to his thigh and hand. He says he suffered burns, blisters, swelling and permanent scarring.

The man's suing Amazon and the charger company for more than $50k.