It's not so much the issue of how long you charge your phone for but how full the battery is.
When you charge it overnight, it likely gets to 100 percent and stays there for hours—which can age your battery faster.
Experts report that lithium-ion batteries (a.k.a the kind that are in your smartphone) age slowest when they're kept at 30 to 50 percent battery life.
Even Apple's website agrees, noting that to extend the life of your battery, it's ideal to keep it half-charged.
While the overnight charging isn't the root of the problem, if you charge your phone on your bed while you sleep, it's a serious fire hazard.
The vents on your phone get blocked by blankets so it can't cool down properly and it ends up overheating and possibly even catching fire.
Make sure your phone is in a well-ventilated area when it's charging, and keep in mind that it shouldn’t be at 100% all the time.
Our tech experts advise people to let their phone's battery drain as much as possible before they start the charging cycle.
Batteries have a sort of memory process and the ability to recharge will weaken over time if you're constantly recharging when you're at 75% or 50% battery life.
And if you're worried about your phone dying during the day, consider a portable charger or wireless charging pad, which tend to charge smartphones much quicker.