US tech giant Apple will pay up to $US500 million ($A763 million) to settle a class action lawsuit in which it was accused of slowing down older iPhones.

The proposed settlement asks Apple to pay the owners of certain iPhone models about $US25 dollars per affected device, according to documents from the San Jose district court in California.

The preliminary settlement still requires a judge’s approval.

While Apple agreed to pay a settlement of at least $US310 million, it stressed the agreement was not an admission of guilt.

The settlement will halt a battle that started in 2017, when some customers noticed their phones with older batteries seemed to perform slower after a software update.

Measurements showed the peak performance of the iPhone processor was diminished on models with older batteries.

Customers said it misled them into thinking their phones needed replacement or new batteries.

The tech giant argued it prevented the phones from suddenly turning off when a battery could not provide enough power.

Apple subsequently lowered the price for the exchange of batteries and issued information to its customers.

The controversy affected iPhone models 6, 6s and 7.