The iPhone’s battery is empty very quickly. I myself have to recharge it every day. Most of us will recharge it during the night, but you’ll spill energy. The iPhone is fully charged within two hours, so there’s no need to keep it on the charger the entire night.
The application BatteryFull can help you save energy. When you start the app while you are charging the iPhone, you’ll here an alarm when the battery is full. That way, you’ll know when the battery is done charging, so you can pull your iPhone from the charger. But during the night, you sleep, so it’s not handy to charge the iPhone during the night when you have the BatteryFull app running at the same time. You might want to charge the iPhone during the evening instead.