Modern smartphones automatically manage charging, while heat remains the biggest threat

Meena Jha

It’s bedtime. You set your alarm, notice your phone is down to 23% battery, plug it in beside the bed and go to sleep. By the morning, it’s been connected to the charger for some seven to eight hours – much longer than it needed to reach 100%, especially if it’s on a fast charger. You may have a vague recollection this could be bad for your phone’s battery. The chemistry that makes lithium-ion batteries rechargeable has a limited shelf life, and it’s shortened by repeated charge–discharge cycles.

In the past, the advice has been simple: don’t leave your phone charging overnight and avoid bringing the battery up to 100% to preserve its lifespan, ideally keeping it between 20% and 80%. In principle, that advice is still sound because the fundamental chemistry of the battery inside your phone hasn’t changed. Regularly draining it to 0% and then filling it up to 100% will shorten its lifespan. However, modern phones have improved battery health management and charging controls. As a result, the answer to whether it’s okay to leave your phone plugged in overnight has become more nuanced in recent years.

Better charging controls

Rather than simply telling people not to charge overnight, modern phones can increasingly manage what happens to the battery during those nighttime hours. Apple has offered optimised battery charging since 2019. This feature learns a user’s daily charging routine and delays charging beyond a certain percentage when the phone is expected to remain connected for an extended period.

Samsung and Google Pixel phones both offer a similar feature. Pixel phones have “adaptive charging” which also learns charging habits and slows charging overnight, aiming to reach 100% shortly before you normally unplug the phone.

Samsung phones have “sleep time protection” which stops charging at about 80% while you sleep and adjusts charging to reach 100% just before you wake.

With the new iPhone 17, Apple has also introduced adaptive power mode, which learns typical battery consumption and anticipates when the user might run low, then adjusts power use to help the battery last through the day.

Setting charging limits

So what about charging only to 80%? Reducing time spent at a high state of charge can help manage battery wear. But manufacturers themselves no longer treat 80% as the only choice. Samsung allows users of their most recent phones to set up battery protection that caps charging at a percentage of their choice: 80%, 85%, 90% or 95%.

Apple’s iPhone 15 and later have a similar feature, allowing users to choose between 80% and 100% in 5% increments. The phone can even recommend a particular limit based on the user’s charging habits. Instead of using adaptive charging, Google Pixel 6a and later devices can simply be set to a limit of 80%, an option that’s ideal for people who usually finish their day with some charge remaining.

Ultimately, not charging your phone fully is a trade-off between reducing battery wear over the longer term and having more charge available day-to-day. If 80% comfortably gets you through the day, a lower limit will make sense. If you’re travelling or facing a long day away from a charger, you may want to use more of the battery’s capacity. Even if you do choose a lower charging limit, your phone may occasionally charge itself to 100% so that the device’s battery readings remain correct.

Whatever you do, avoid heat

While all these new charging features can prolong the life of the battery, they don’t really address another important factor: heat. The chemicals in lithium-ion batteries are sensitive to high temperatures and will degrade over time if stored in hot conditions, especially if they’re also being charged at the same time. Phones themselves increasingly respond to heat too, with charging limitations kicking in when the device detects high temperatures. The general advice here hasn’t changed. Always keep your phone away from excessive heat, including leaving it in a hot car or in direct sunlight. If charging at bedtime, make sure you’re not tucking your phone under a pillow or other bedding which could trap heat and risk overheating the device.

So, can you charge your phone overnight?

For most people using a modern smartphone, the answer is yes. The phone manages charging automatically, and you don’t need to wake in the middle of the night to unplug your phone at exactly 80%. Instead, check what your phone offers and use optimised, adaptive or sleep-aware charging if it suits your routine. Consider a lower charge limit if you don’t need 100% every day. Above all, avoid excessive heat. Even though phone batteries still aren’t immune to ageing, we now have more options to try and prolong their life with smart charging features – so it’s a good idea to check your settings and let the technology do some of the work.

(The writer is a computer science and IT researcher at Central Queensland University, Australia)