No, it's not bad. Modern phones stop pulling power once they hit 100%, so the real risk is heat, not the number of hours plugged in.
The overnight-charging myth comes from old nickel-based batteries that really did degrade from being left on the charger. Lithium-ion, the battery in every phone sold today, works differently.
What actually shortens battery lifespan is time spent hot and time spent sitting at 100% under a warm blanket or pillow, not the simple act of charging while you sleep.
Once the battery reaches full, the charging circuit cuts the current and switches to trickle top-offs that only kick in when the level drops a percent or two. The phone isn't receiving a constant flood of power for eight hours.
Lithium-ion cells lose capacity fastest when they sit warm. Charging under a pillow, in a tight case, or on a soft surface that blocks airflow can push the phone several degrees hotter than it needs to be. Consistent exposure above about 95°F/35°C speeds up capacity loss more than years of normal overnight charging ever will.
iPhones (Optimized Battery Charging) and most Android phones (Adaptive Charging) learn your wake time and delay the last 10-20% until shortly before your alarm, so the battery spends less time sitting at full. Turning this on is one of the few settings worth flipping.
A phone that gets uncomfortably hot to the touch, swells, or shows a battery health drop below 80% well before 2-3 years of typical use deserves attention. Otherwise, plug it in and go to sleep.
Charging overnight isn't the problem people think it is, heat and cheap accessories are. Turn on optimized charging if your phone offers it, keep it out from under blankets, and you're fine.
Only slightly, and mainly through heat exposure rather than the charging itself. A phone charged overnight for 2-3 years typically still holds around 80% of its original capacity if kept cool.
No need. The charging circuit stops the flow automatically, so unplugging manually makes no measurable difference for a phone charged for one night.
Partial charges, like 30% to 80%, are gentler on lithium-ion cells long term, but overnight charging isn't harmful enough to require changing your routine.
Yes. It delays the final charge percentage until close to your usual wake time, reducing the hours the battery spends sitting at full capacity.