I usually charge my phone all day and night long. All day long, because at work I connect my phone with my laptop, and all night long because when I go sleep, the phone will be charged overnight too.
But I got worried this may reduce battery life. So I went searching online, and the best article I can come up for best practice for charging Apple device is this. In the article, it just says that the device is smart, and can automatically stop the charge once it's almost full, to prevent overcharging. Does that mean it's actually completely okay for me to charge the phone all day long? I still can't find any article that can give me the straight answer to this question.
Best Answer
This questions risks inviting a lot of opinion, which also explains why it seems you can't find an article that can gives you a straight answer.
However, to try and keep this to the facts, I refer you firstly to what Apple has to say about their batteries. You should also read this.
In a nutshell, the key indisputable points are:
Apple lithium-ion batteries use fast charging to reach 80% of their capacity and then switch to slower trickle charging to complete the charge.
Ambient temperature is one of the biggest factors in battery health/life. iPhones are designed to work at their best when ambient temperatures are between 0° to 35° C (32° to 95° F).
Also, the latest research confirms one of the most important determinants of what ruins a battery is time. (You could purchase a brand new iPhone battery and leave it unused in its original packaging for five years and then find its capacity is nowhere near what it should be when you start using it)
Basically, you can continue to do as you have been without fear of causing damage to your iPhone battery.