Battery failure occurs when a battery can no longer hold a charge or provide the necessary power to operate a device. This can happen due to various reasons, including age, excessive heat, or physical damage. Common signs of battery failure include slow charging, reduced runtime, or the device not turning on at all. When a battery fails, it may need to be replaced to restore functionality. Regular maintenance, such as avoiding extreme temperatures and not overcharging, can help prolong battery life. Understanding the signs of battery failure can assist users in taking timely action to prevent further issues with their devices, such as smartphones or laptops.