This is according to UK repair company, mendmyi, who discovered the unauthorized third-party chargers can actually damage the U2 IC chip on the logic board of the iPhone 5. What this does is that when damaged, it could cause the phone to fail to boot up or even charge past 1% on battery life once the battery has drained.
This means that you’re pretty much stuck with a lemon should that particular component be damaged. Given that the component also controls the sleep/wake button, USB functions, and regulates the charging power, safe to say it is a pretty important component that you do want to damage because you’d rather not spend that little bit extra on an official iPhone charger.
Mendmyi also found that replacing the battery doesn’t really help much since the component has been damaged, meaning that the issues from before could resurface again. It is unclear if unauthorized third party chargers have the same effect on other iPhones or other branded phones, but given the horror stories we’ve read, why take that chance?