A recent study by OpinionWay for Assurance Prévention found that 62% of French people regularly leave their smartphones plugged in overnight. In the past, this practice was thought to be harmful due to older battery technology, which could overheat or degrade more quickly when left charging for long periods. However, modern smartphones now use advanced Battery Management Systems (BMS), which automatically stop charging once the battery is full. These systems help prevent overcharging and reduce potential damage to the battery. Apple and Samsung have both introduced features designed to further protect battery health. Apple’s Optimized Charging, available since iOS 13 in 2019, pauses charging at 80% and resumes shortly before the user’s usual wake-up time. This helps reduce stress on the battery. Similarly, Samsung enhanced its Battery Protection feature with One UI 6.1 in January 2024, offering an adaptive charging system that works in a comparable way. These technologies aim to extend battery life by avoiding prolonged full charges. The main concern for battery health isn’t the act of charging overnight itself, but the heat generated during the process. According to a 2018 review published in ScienceDirect, lithium-ion batteries—used in most smartphones—can degrade more quickly when exposed to temperatures above 35 degrees Celsius. Charging a phone in environments that trap heat, such as under a pillow or in a thick case, can significantly shorten battery life. The study also found that 84% of French people often engage in at least one risky behavior with their lithium-ion batteries. Common risks include using uncertified chargers (55%) and charging near flammable fabrics (52%), which are more prevalent than the risk of overnight charging. To help preserve battery health, experts recommend charging devices between 20% and 80% on a hard, ventilated surface using the original charger. This approach minimizes heat buildup and reduces the risk of chemical degradation in the battery. Following these guidelines can help extend the lifespan of a smartphone’s battery and ensure safer charging habits.