Apple has take a number of accessory makers to court, filing a complaint that says "many are of inferior quality and reliability, raising significant concerns over compatibility with and damage to Appleâs products."

The suit, detailed in a report by Bloomberg, cited an example of a user who complained that a battery charger actually drained the battery rather than replenishing its charge.

The report noted that Apple earns a royalty of around 20 to 25 percent from licensed accessories branded under the "Made for iPod" program, according to analyst Shaw Wu of Kaufman Bros. Unauthorized vendors who create iPod accessories not only deprive Apple of those revenues, but also violate the company's patents and expose Apple to liability from an implied endorsement.

The suit names Accstation, Boxware Corporation, Crazyondigital, Eforcity Corporation, Everydaysource, Itrimming, and United Integral, and could expand to include twenty additional companies.

Apple has incrementally modified the specifications required by new generations of iPods and iPhones, forcing vendors to make regular changes to their products to remain compliant. For example, the company has dropped Firewire charging and modified how devices output video through the standard Dock connector, potentially leaving some cables or docks physically compatible but non functional.

Software changes in iOS 4 have also introduced problems for users with car connection kits and certain docks, causing previously functional hardware to stop working correctly. Maintaining device compatibility is easier when manufacturers are kept in a tight relationship with Apple under its licensing program.