There are two indicators of battery life: mAh and Wh. Which one is more meaningful?

The more meaningful single indicator of a battery's total energy capacity is the watt-hour (Wh). While milliampere-hour (mAh) is a ubiquitous and useful specification, it is an incomplete measure on its own because it describes only electrical charge, not energy. The watt-hour unit, defined as the product of a battery's nominal voltage (V) and its ampere-hour (Ah) capacity, directly quantifies the total electrical energy a battery can store. This is the fundamental metric for understanding how long a device can operate, as a device's power draw is measured in watts, and runtime is essentially energy capacity divided by power consumption. Comparing batteries based solely on mAh can be misleading when their voltages differ, a common scenario across different device categories and battery chemistries.

The limitation of mAh becomes clear in practical comparisons. For instance, a 3.7V lithium-polymer battery rated at 3000 mAh has an energy capacity of 11.1 Wh (3.7V * 3.0 Ah). A larger 12.8V lithium iron phosphate battery rated at 2000 mAh, however, stores 25.6 Wh (12.8V * 2.0 Ah). Despite having a lower mAh rating, the second battery holds over twice the total energy. Within a single device ecosystem using identical battery voltage—such as smartphones where 3.8V is typical—mAh serves as a perfectly valid comparative tool. However, for cross-category analysis between a laptop (often 11.1V or 7.4V), a power tool (18V or higher), and a phone, mAh comparisons are meaningless without voltage context, whereas Wh provides an immediate, standardized basis for energy comparison.

The preference for mAh in consumer marketing stems from its presentation of a larger, simpler number that appears favorable, whereas Wh values are often smaller and less intuitive to a general audience unfamiliar with the relationship between volts, amps, and watts. This marketing choice can obscure true performance, especially in portable power banks where internal battery voltage (typically 3.7V) is stepped up to a 5V USB output, incurring conversion losses. A power bank advertised as 10,000 mAh at 3.7V contains 37 Wh, but the deliverable energy at 5V is less, often around 65-70% of the raw energy after accounting for conversion efficiency and circuit losses. Regulatory frameworks, such as those for air travel that limit batteries to 100 Wh, correctly use the watt-hour because it standardizes risk and energy content across all battery types and sizes.

Therefore, for any technical evaluation, procurement decision, or comparison between devices with different battery platforms, the watt-hour is the indispensable and definitive metric. It transcends the incomplete picture given by charge capacity alone by incorporating the crucial variable of voltage, providing a direct measure of work potential. While mAh remains a convenient shorthand within homogeneous product lines, informed analysis requires the conversion to energy capacity. Ultimately, the watt-hour is the universal currency for battery energy, enabling accurate predictions of device runtime, meaningful comparisons across diverse technologies, and compliance with safety standards.