Has your iPhone started to run slower? If this is the case, then we have some tips to help speed it up.
How to speed up a slow iPhone

1. Check the battery status of your iPhone

Most likely, you already know about Apple's dubious decision to add to iOS 10.2.1 a feature that slows down old iPhone's to avoid their sudden shutdowns under heavy load.
This feature is available in Phone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus, iPhone SE (iOS 10.2.1 and newer), iPhone 7 and iPhone 7 Plus (iOS 11.2 and newer).
If you have one of these models, it would not hurt to check the status of your battery. There are several ways to do this. 
The power management function monitors the temperature of the device, as well as the state and resistance of the battery. It is important to note that this function is only activated if necessary and will not slow down your iPhone if the battery status is normal.
If the power of your battery has fallen below 80% of the initial, it must be replaced. However, we recommend waiting until Apple releases the iOS update, which will provide more information about the battery status.

# 2. Restore your iPhone

Perhaps the reason for the slow operation of your iPhone is not in the battery. If the smartphone is running stably slowly, then maybe not the battery is at fault.
Some users helped the recovery of the iPhone, after which he again began to work quickly.
We even recommend setting it up as new. It can solve all the problems. Moreover, recovery helps to solve many problems of the system. Older models like the iPhone 6 and the iPhone 6 Plus have survived at least two large iOS upgrades, and the recovery can help get rid of unnecessary residual files.
This is not the most convenient method, but recovery is free, so it's worth trying. If it does not help, you will have to change the battery.