The legal action comes
after Apple's revelation it may at times dynamically manage the maximum performance of some older iPhone models with chemically aged batteries in order to prevent the devices from unexpectedly shutting down, an issue that can be made worse by cold temperatures or a low charge.
...
Keep in mind that Apple is not permanently or persistently slowing down older iPhones. Even if your iPhone is affected, the performance limitations only happen intermittently, and only when the device is completing demanding tasks.