How Should You Charge a Phone to Keep the Battery Healthy?

Short answer: Keep a modern phone between roughly 20% and 80% charge, keep it cool, and leave optimised or adaptive charging switched on. Overnight charging is fine on any phone made in the last five years; heat and long spells at 100% do far more damage than the number of charges.

Lithium-ion cells age through two mechanisms: cycles and stress. You cannot avoid cycles, but you can avoid stress — high temperature, sitting at a full charge, and draining to empty. Manufacturers now rate batteries at about 80% of original capacity after 500 to 1,000 full cycles, which for most people is two to three years.

What actually shortens battery life

• Heat above about 35°C, including charging inside a car on a sunny day or under a pillow.
• Sitting at 100% for hours every night without optimised charging enabled.
• Repeatedly running down to 0% and leaving the phone flat for days.
• Fast charging while gaming, which stacks two heat sources at once.

Settings worth turning on

1. iPhone: Settings > Battery > Charging > Optimised Battery Charging, or the 80% limit on newer models.
2. Android (Pixel, Samsung): Adaptive Charging or Battery Protection in battery settings.
3. Remove thick cases while fast charging if the phone gets noticeably warm.
4. Use a charger from a known brand; cheap unbranded units run hotter and less stable.

Charging habits compared

When to replace the battery

Replace it when maximum capacity drops below about 80% and the phone shuts down early or throttles. A battery swap costs a fraction of a new phone and usually restores full-day life.