eh.. Why do manufacturers speak mAh instead of watts??

people get very annoyed when they know what that really means. Say for example, every power bank available says 10,000 mAh, or 20,000 mAh (or whatever), but all those are at 3.6 volts (not at 5 volts). As most of the other specs is in 5 volts, most people don't even know this.

> eh.. Why do manufacturers speak mAh instead of watts??

Neither amp-hours nor watts measure energy. Watts measure power, which is irrelevant for a laptop battery, and amp-hours measure nothing unless you know the battery voltage.

The spec for a battery should be in joules or watt-hours.

Enough with the watt-hours already! Let's all just measure batteries using Joules, we have a unit specifically for quantities of electrical energy.

A watt-hour is 3600 Joules, which is not a nice round number, but it's fairly easy to remember. At least they're both proper units of energy.

My thinkpad battery holds 5e23 eV of energy.

Both because using mAh in consumer electronics became common with NiCd and NiMH cells before they broke the 1A limit, and today because it allows writing a bigger number on ads.