Smartphone Battery Care: Experts Advise Against Full Charges and Extreme Temperatures
Most smartphone users charge their devices either by waiting for a near-complete discharge or by leaving them plugged in overnight. However, these common practices are not ideal for modern lithium-ion batteries, which degrade based on factors including temperature, charge level, charging speed, discharge depth, and time spent at maximum voltage. Recent research indicates that a combination of high temperature, high charge level, and rapid charging significantly accelerates battery degradation.
Experts recommend avoiding keeping a phone constantly at 100% charge. Unlike older nickel-cadmium batteries, lithium-ion batteries do not have a "memory effect," making full discharges unnecessary and potentially harmful. The optimal daily charge range is generally between 20% and 80%. While charging to 100% is not inherently damaging, prolonged periods at maximum charge accelerate aging. To address this, manufacturers are incorporating charge limiters. For instance, Apple's iPhone 15 and newer models allow users to set a charge limit between 80% and 100%, while Google Pixel phones offer an "80% Max" mode to extend battery lifespan.
Overnight charging is generally safe, as device electronics prevent overcharging. However, leaving a phone plugged in for hours near full charge can still be detrimental. Modern smartphones employ features like Apple's Optimized Battery Charging and Google's Adaptive Charging to manage this by delaying the final charge to 100% until just before the user typically disconnects the device. These systems learn user habits over time to optimize charging schedules.
Extreme heat is identified as a major battery enemy. Apple advises against exposing devices to ambient temperatures above 35°C, warning that charging in high heat can cause irreversible damage. This is particularly relevant in hot climates like Israel, where a phone left in a car can overheat significantly, especially when combined with navigation or mobile data usage. Research confirms that high temperatures above 35°C lead to increased internal resistance and reduced battery performance. Charging a hot phone, whether in the sun, on a hot surface, or under a pillow, should be avoided.
Fast charging, while convenient, can increase battery load and generate additional heat, contributing to degradation. While modern smartphones regulate charging speeds, consistently using the fastest mode for extended charging periods is less ideal than a moderate speed, especially if it reduces heat. Wireless charging also presents a heat-related drawback due to energy loss during transmission, potentially exacerbating temperature issues when the phone is in use simultaneously. For daily overnight charging, optimized modes are recommended, and switching to wired charging or a less powerful mode might be necessary if significant heat is generated.
Instead of waiting for a 0% discharge, it is more beneficial to charge the phone when it reaches 20-30%. A full charge cycle is defined by the total energy consumed, not individual charging sessions. For example, charging from 30% to 80% twice does not equate to two full cycles. While charging to 100% is acceptable when maximum battery life is needed, consistently keeping the phone at 100% should be avoided unless necessary. The key to battery longevity lies in avoiding excessive heat, prolonged 100% charges, frequent deep discharges, and utilizing built-in charging optimization features, rather than adhering to strict percentage rules.
