Lithium-ion batteries are sensitive to their own version of stress.
If you leave your phone plugged in when it's fully charged you will likely add to the battery's stress.
When your phone reaches 100 per cent it gets "trickle charges" to keep it at 100 per cent.
Unfortunately, this keeps the battery in a high-stress and high-tension state which wears down the chemistry inside the smartphone.
Battery university compared it to relaxing the body after exercise.
"Li-ion does not need to be fully charged, nor is it desirable to do so. In fact, it is better not to fully charge, because a high voltage stresses the battery", wearing it away in the long run, it said on Battery University.
They also suggested not charging your phone over a long period of time, instead, charging it regularly throughout the day.
Charging your phone when it loses 10 per cent battery is the best scenario. According to Battery University, the batteries will remain a lot happier and keep their long-term lifespan intact.
Keeping your phone cool will also help preserve it's long-term battery lifespan and suggests to remove it from any causes that may insulate heat while charging.
Battery University also recommends you keep your phone out of direct sunlight.