In that update, the company tweaked the iPhones 6, 6s and SE to instead slow down the processor when the voltage dropped.
"For the sake of its loyal fans, Apple has to take responsibility over the slowing iPhones", Park Soon-jang, an official at the advocacy group told Reuters by phone on Friday.
The Seoul Central District Prosecutors' Office declined to comment when asked if it would launch an investigation into Apple following the complaint from the consumer group.
On December 20, Apple admitted it slows down older iPhones to offset problems in aging lithium-ion batteries, which also explains why Futuremark found no performance discrepancies in phones running different versions of iOS.
Apple has repeatedly denied it engages in planned obsolescence.More news: US crude falls 2 cents, closing at $63.95 after inventories slip
The company said the update will allow users to check the health of their battery and choose whether to turn off the part of the iPhone software that slows it down to preserve its battery life, Xinhua news agency reported. Cook noted, however, that such a move would put users at risk for unexpected shutdowns as their battery ages.
"We deeply apologize for anybody that thinks we had some other kind of motivation", Cook told ABC. The advocacy group, Citizens United for Consumer Sovereignty, is accusing Apple of destruction of property and fraud.
Apple has announced its plan to release a software update to all its iPhone models to address allegations that the company deliberately downgraded older models to encourage users to buy new phones.
The group also represents about 120 plaintiffs in a civil damage suit against Apple filed earlier this month.
It's the latest sign of trouble for Apple over the power-management feature it introduced in iOS 10.2 and again in iOS 11 to counter unexpected shutdowns on iPhones with aged batteries. To offset the complaints, Apple reduced the cost of replacement batteries to $29 in a public apology to its customers.