Is it bad to charge a phone overnight?

This advice has outlived the technology it was about. Old nickel batteries genuinely suffered from being left on charge; the lithium-ion cells in every modern phone are managed by circuitry that will not overcharge them. The real causes of battery ageing are different and less obvious.

Safety

Step by step

1. Understand what happens when a phone reaches 100%.Charging stops. The phone runs from the mains and lets the battery sit, topping it up only when it drifts down a little. It is not being force-fed current all night.
2. Know what actually ages a battery.Heat, total charge cycles, and time spent at very high or very low charge. A cell held near 100% for hours degrades faster than one held around 50%, and heat accelerates everything.
3. Turn on optimised or adaptive charging.Both iPhone and Android have a setting that charges to around 80%, then finishes just before you normally wake. It removes almost all of the time spent at full charge and needs no thought once enabled.
4. Use an 80% charge limit if your phone offers one.Newer phones let you cap the charge. Worth using if you are usually near a charger; less so if you regularly need a full day of battery.
5. Keep it cool while charging.Off the bed, out from under a pillow, and out of a thick case if it gets hot. Fast charging plus a warm room plus a case is where the real damage happens.
6. Do not obsess about the 20-80 rule.Keeping a battery between 20% and 80% does extend its life measurably, but a phone you are anxious about using is worse value than a battery that lasts three years instead of four.
7. Ignore the advice about full discharges.Running a lithium battery flat to 'recalibrate' it is a nickel-battery habit. Deep discharges stress lithium cells; partial charges are actively better for them.
8. Use a decent charger.The manufacturer's, or a reputable brand supporting the phone's charging standard. Very cheap unbranded chargers can deliver poor-quality power and are the real safety concern here.
9. Check battery health rather than guessing.Both platforms report a maximum capacity percentage in settings. Below about 80% is when a battery starts to feel genuinely poor, and that is the number to act on.
10. Store a spare device at around half charge.A phone or tablet left in a drawer for months should be at about 50%, not full and not flat. Storing at either extreme is what kills unused batteries.

Tips

• Wireless charging generates more heat than a cable for the same charge. Fine occasionally, worth avoiding as the overnight default.
• If the phone is hot in the morning, something is wrong — an app running all night, or a case trapping heat. That matters more than the charging schedule.
• Battery replacement is usually far cheaper than a new phone and restores most of what people think is a slow phone.

Common mistakes

• Charging under a pillow or on a bed — Bedding insulates the phone so it runs hot all night, which is the single biggest cause of battery degradation and the one genuine fire risk.
• Running the battery flat regularly to 'condition' it — That advice applies to nickel batteries, which phones stopped using two decades ago. Deep discharges stress lithium cells rather than helping them.

If it doesn't work

Questions people ask