Is it actually bad to leave a phone charging overnight?

The short answer is that it is generally safe for modern smartphones, but it can accelerate battery aging over the long term.

Here is why:

• Smart charging: Modern smartphones are designed with built-in protection. Once your battery hits 100%, the phone stops pulling power from the charger to prevent overcharging.
• Trickle charging: Throughout the night, the battery level may drop slightly due to background processes. When it dips to 99%, the phone will pull a tiny amount of power to top it back up to 100%. This "trickle charging" can keep the battery in a state of high stress.
• Heat: Heat is the biggest enemy of lithium-ion batteries. If your phone is tucked under a pillow or in a case that traps heat while charging, the combination of the charging process and the trapped heat can degrade the battery's health more quickly.

How to extend your battery's lifespan:

• Use Optimized Charging: Most modern phones (like iPhones or Androids) have a setting called "Optimized Battery Charging" or "Adaptive Charging." This feature learns your sleep habits and holds the charge at 80% until just before you wake up, reducing the time your battery spends at 100%.
• Keep it cool: Ensure your phone is on a hard, flat surface while charging so heat can dissipate effectively.
• Don't worry too much: While avoiding overnight charging is better for the battery's long-term capacity, most people replace their phones every few years anyway. Modern batteries are durable enough that you likely won't notice a significant difference in daily performance for a long time.