Apple Inc has agreed to pay up to US$500mil to settle litigation accusing it of quietly slowing down older iPhones as it launched new models, to induce owners to buy replacement phones or batteries.

The preliminary proposed class-action settlement was disclosed on Friday night and requires approval by US District Judge Edward Davila in San Jose, California.

It calls for Apple to pay consumers US$25 per iPhone, which may be adjusted up or down depending on how many iPhones are eligible, with a minimum total payout of US$310mil .

Apple denied wrongdoing and settled the nationwide case to avoid the burdens and costs of litigation, court papers show.

The Cupertino, California-based company did not immediately respond on Monday to requests for comment.

Friday's settlement covers US owners of the iPhone 6, 6 Plus, 6s, 6s Plus, 7, 7Plus or SE that ran the iOS 10.2.1 or later operating system. It also covers US owners of the iPhone 7 and 7 Plus that ran iOS 11.2 or later before Dec 21, 2017.

Consumers contended that their phones' performance suffered after they installed Apple software updates. They said this misled them into believing their phones were near the end of their life cycles, requiring replacements or new batteries.

Apple attributed the problems mainly to temperature changes, high usage and other issues, and said its engineers worked quickly and successfully to address them. Analysts sometimes refer to the slowing of iPhones as "throttling".

Lawyers for the consumers described the settlement as "fair, reasonable, and adequate".

They called payments of US$25 per iPhone "considerable by any degree," saying their damages expert considered US$46 per iPhone the maximum possible.

The lawyers plan to seek up to US$93mil , equal to 30% of US$310mil , in legal fees, plus up to US$1.5mil for expenses.

Following an initial outcry over slow iPhones, Apple apologised and lowered the price for replacement batteries to US$29 from US$79 .

 - Reuters