Is It Safe to Charge My Phone Overnight? (Samsung & iPhone Explained)
Many people plug in their phone before going to sleep and leave it charging until morning.
Some say it damages the battery, others say modern phones can handle it.
Here’s the real answer based on what we see daily in our NZ repair shops.
1. Most Battery Issues We See Start From Heat — Not “100% Charging”
In Auckland and Christchurch, many customers come in with batteries that drain fast, swell, or shut down randomly.
A surprising number tell us: “I leave it plugged in every night.”
Good news: overnight charging itself is usually safe.
Bad news: heat during extended charging absolutely kills battery life.
2. You’ve Probably Experienced These Problems
Common patterns from real users:
- Phone feels warm when you pick it up in the morning.
- Battery health on iPhone dropping faster than expected.
- Samsung showing battery warnings or sudden shutdowns.
- Using cheap chargers that get hot overnight.
- Leaving the phone under pillows or blankets while charging.
If any of this sounds familiar, the phone isn’t failing — the charging habits are hurting it.
3. What We Recommend to Customers in Our Shop
3.1 If You Charge Overnight, Do It Safely
- Use a quality charger (Apple, Samsung, Belkin, Anker).
- Keep the phone uncovered — no blankets, no pillows.
- Do not stack the phone on books or soft materials.
- Remove thick or heat-trapping cases if possible.
- Place the charger on a hard, cool surface.
3.2 Samsung Users: Turn On “Protect Battery”
Limits charging to ~85%, reducing heat and prolonging lifespan.
Settings → Battery → More Battery Settings → Protect Battery
3.3 iPhone Users: Use “Optimised Charging”
iPhone learns your routine and avoids staying at 100% for hours.
Settings → Battery → Battery Health & Charging → Optimised Charging
3.4 Avoid Fast Charging Overnight
Fast chargers pump higher voltage early in the cycle. Use them during the day;
for overnight, a slow 5W–10W charger makes less heat.
4. Technical Truth: Modern Phones Stop at 100%, But Heat Continues
Apple and Samsung both use charging controllers that stop current once the phone hits 100%.
So overcharging isn’t the real danger — trickle charging + heat is.
Scientific studies (Samsung SDI Battery Tech Docs, Apple Battery Chemistry Guide) show:
- High temperature (over ~35°C) accelerates chemical degradation.
- Staying at 100% for hours creates surface-level stress on lithium cells.
- Repeated heat cycles cause swelling and rapid capacity loss.
That’s why some people lose 10–15% battery health in a single year even with light usage.