Over time, the capacity of iPhone batteries deteriorates leaving you in a constant state of charging your phone. The lifespan of smartphone battery normally last around 2 years. Although naturally with age, devices do get slower and batteries die a lot quicker, there are ways for you to try and get every last bit out of your Smartphones battery life before you have to replace it with a new one.
There's nothing more frustrating than looking at your phone to realise you're almost out of battery and it's only 11 am.