Charging your phone overnight? Here's what it does to your battery

Leaving your smartphone plugged in overnight is no longer necessarily a threat to its battery life, thanks to improved charging technology. Modern smartphones can manage charging automatically, reducing the time the battery spends at full capacity.

However, battery health still depends on how a phone is charged, the temperature it is exposed to and the amount of time it spends at a high charge level.

The traditional advice has been to avoid charging a phone to 100% or letting its battery drain completely to 0%. Instead, keeping the charge between 20% and 80% has been considered a way to extend battery life.

That recommendation is based on the chemistry of lithium-ion batteries, which gradually lose capacity through repeated charge-discharge cycles. Regularly draining a battery completely and then charging it to full capacity can accelerate this deterioration.

But smartphone manufacturers have introduced features that automatically manage charging, making overnight charging less concerning than it once was.

How smartphones manage overnight charging

Modern smartphones increasingly use adaptive charging systems to reduce the time batteries spend at full capacity.

Apple introduced optimised battery charging in 2019. The feature learns a user's charging routine and delays charging beyond a certain level when the phone is expected to remain connected to a charger for an extended period.

Samsung and Google Pixel devices offer similar features.

Google Pixel phones use "adaptive charging" to learn a user's charging habits and slow charging overnight, aiming to reach 100% shortly before the phone is usually unplugged.

Samsung's "sleep time protection" feature holds the charge at around 80% during sleep and adjusts charging so the battery reaches 100% closer to the user's usual waking time.

Apple has also introduced adaptive power mode with the iPhone 17. The feature learns typical battery consumption patterns and anticipates when the user might run low, adjusting power use to help the battery last through the day.

These technologies mean users no longer need to wake up in the middle of the night to disconnect their phones at a particular percentage.

Should you limit your phone's charge to 80%?

Limiting the time a battery spends at a high charge level can help reduce battery wear. However, manufacturers now offer more flexible charging limits rather than treating 80% as a universal rule.

Samsung's latest smartphones allow users to activate battery protection and choose a maximum charge level of 80%, 85%, 90% or 95%.

Apple's iPhone 15 and later models offer similar controls, allowing users to set charging limits between 80% and 100% in five-percentage-point increments. The phone can also recommend a limit based on charging habits.

Google Pixel 6a and later devices allow users to set an 80% charging limit instead of using adaptive charging.

The choice ultimately comes down to how much battery capacity a person needs during the day.

If an 80% charge is enough to get through the day, setting a lower limit may help reduce long-term battery wear. Those travelling or spending long hours away from a charger may prefer to use the full battery capacity.

Even with a lower charging limit, a phone may occasionally charge to 100% to keep its battery readings accurate.

Heat remains a major threat to battery health

While modern charging features can help extend battery life, they do not eliminate the damage caused by excessive heat.

Lithium-ion batteries are sensitive to high temperatures, which can accelerate chemical degradation over time. The risk is particularly significant when a battery is exposed to heat while charging.

Smartphones increasingly respond to high temperatures by limiting charging speed