iOS 11.3 was released today. It offer a new feature, allowing you to check the maximum battery life capacity and turn off automatic performance throttling if your battery is old.
However if you do turn off performance throttling you may experience unexpected shutdowns as the battery is no longer able to supply enough current to support full speed.
If your maximum capacity is less than 80% or your peak performance has been throttled automatically, then come to Bournemouth iPhone Repairs to get your battery replaced using a genuine Apple part. You’ll be able to give your iPhone 6 or 6S a new lease of life letting it run at full speed again. Txt 07887803967 to get a quote.