Engadget Explains Why Battery Capacity and Battery Life Are Not the Same

Capacity is expressed in milliampere hours for small devices such as phones and power banks, or watt hours for larger devices such as laptops. Battery life is typically measured in hours. Higher capacity theoretically means more stored energy and longer runtime per charge. For example, a phone with a 5,000mAh battery should, on paper, last longer than one with a 4,200mAh battery. Similarly, a power bank's capacity should indicate how many times it can charge a phone. Engadget noted that an iPhone 18 Pro in the US model has a battery capacity of 4,288mAh, meaning a 10,000mAh power bank could theoretically charge it a little more than two full times. Charging is not perfectly efficient, however. Normal charging usually loses 20 to 30 percent, and fast charging or wireless charging generates more heat and therefore has even higher loss percentages.

Real-world battery life depends on many factors beyond capacity. A laptop with a large battery playing modern games at high graphic settings will likely deplete faster than a laptop with less capacity used only for word processing. Screen size matters, too: an iPad has a bigger battery than an iPhone but also a much larger screen that uses more energy. Temperature affects battery life, as a phone battery may drain more quickly when taking photos outside on a hot summer day. Operating system and hardware efficiency also play a part, which is why Apple silicon MacBooks last longer than older Intel models, according to Engadget.

Battery life can never be a perfect measurement because people do not use their devices exactly the same way each day. Companies often provide battery life numbers based on hours of playing video files, and Apple adds a typical battery life number for some newer devices. As batteries age, their capacity decreases. After 1,000 charge cycles, a battery life icon showing 100 percent does not mean what it did when the device was new.

Battery health is tied to charge cycles. One cycle occurs every time a battery goes from 100 percent to zero percent charge, though those discharges do not have to happen all at once. Starting with the Google Pixel 8a, Pixel devices are rated to retain up to 80 percent battery capacity for 1,000 full charge cycles. If a user adds 100 percent charge to a device daily, the battery may need replacement in about 2.5 years, Engadget said.

Engadget offered several ways to extend battery life. Users can keep devices updated to the latest OS, lower screen brightness, shut down unnecessary background activities and check which apps drain the battery most. For long-term battery health, the article recommends keeping the battery between 20 and 80 percent as much as possible rather than waiting until it completely depletes and charging up to 100 percent. A battery will chemically age over time regardless. Once capacity reaches 80 percent, it is a warning sign that the battery should be replaced. On many smartphones, battery health percentage can be checked in the Settings menu under the Battery section, and some devices may send a warning notification when the battery is significantly degraded. With normal use, Engadget said, a battery should last a long time; the article's author reported that their iPhone 17 Pro was still at 94 percent battery health after 316 full charge cycles over the last year.

Some of the latest devices are switching to silicon-carbon batteries that can pack larger battery capacities into smaller spaces, so users do not have to accept a heavier or thicker device to enjoy long battery life. But it could be a while before these batteries become mainstream, Engadget said.