These products "may not be designed properly and could result in safety issues," Apple writes. Instead the company is recommending first-party power adapters, and directing people to go to an Apple store or authorized service provider for replacement batteries.
Apple often charges high prices for first-party accessories and repairs, which can lead many people to turn to outside sources. While certified third-party accessories are typically safe, unauthorized and/or counterfeit products have been known to work poorly or even cause fires.
Underwriters Laboratories —better known as UL —recently tested 400 fake Apple chargers, and found that 99 percent of them were unsafe. In October Apple filed a lawsuit against one counterfeit vendor, Mobile Star, accusing it of violating copyrights and trademarks through sales on Amazon and Groupon.
Amazon is reportedly poised to engage in a major crackdown of its own, creating a registry of recognized sellers that vendors will have to match against to get their inventory on sale. In its Mobile Star suit, Apple claimed that almost 90 percent of Apple accessories sold as genuine through the "Fulfillment by Amazon" program were fake.