SHANGHAI, Jan. 15 (Xinhua) -- The Shanghai Consumer Council said Monday it has sent an inquiry letter to Apple over the slow-down of older iPhones after an iOS update, demanding a reply before Friday.

The council demanded the cause of the performance and remedy measures as well as complete information regarding the interests of consumers.

The council said it received 2,615 complaints on Apple products and services in 2017, compared with 964 complaints in 2015.

In late December, Apple apologized for the slow-down of the of old iPhones with older batteries amid lawsuits and consumer outrage. It said the company will cut the price of out-of-warranty iPhone battery replacements from late January 2018 to December.