I have a habit of switching off my phone and putting it on charging. Like my Nokia and Motorola phones, my iPhone doesn't display how much battery has been charged when I connect it to the charger and switch it off. So that's why I asked the question.
Go to Settings, then General, then Usage, the Battery Percentage ON. When you plug in your iPhone, the display lights up. Check the battery percentage in the upper right of your screen before powering down.
Battery percentage is already on and yes I do check its percentage in upper right corner before powering down. I wanted to know about it displaying battery percentage on charging after switcing it off.