How many hours does a modern laptop battery last?

How to get close to this number

Design intent sets the answer. A portable computer has to last a working day away from a socket or it fails at its basic purpose, and manufacturers target exactly that. Whenever a consumer device figure could have been anything, ask what behaviour it has to support — battery life is almost always designed to a human schedule rather than to a technical limit.

The explanation names the counterintuitive cause of the improvement: not bigger batteries but processors that draw almost nothing when idle. Battery chemistry has improved slowly and incrementally, while power management has improved enormously, so the gain came from the demand side rather than the supply side. That is the same shift that made smartphones possible at all.

Treat the figure as a marketing condition rather than a measurement. Quoted battery life assumes light use at moderate screen brightness, and real-world figures under a heavy workload are often half of it. Manufacturer specifications and independent review figures routinely disagree, which is why the source line here names both.