Apple says it will give iPhone users the ability to turn off a software tool that can slow down device performance. The change is expected to come this spring with the release of Apple’s latest mobile operating system update, iOS 11.3. The announcement followed heavy criticism and user anger when it became public that Apple had secretly been slowing down operating systems of older iPhones. The slowdown issue was first pointed out in internet reports. Apple admitted the practice in December. In an explanation, the company said it only took the action to prevent some aging batteries from failing and completely shutting devices down.