A laptop battery pack is composed of several battery cells that are wired together in series. By combining the cells higher volumes of energy can be delivered to your laptop computer. The number of cells is a indicator of how long a battery can last. But not all cells are created equally. To find out how how much energy a battery can store, you should look at the mAh rating.
mAh stands for Milliamp Hour, which is a technical term for how much power a particular battery will hold. Batteries with a higher mAh value will theoretically last longer before requiring a recharge.
Batteries with the same number of cells, can have different mAh ratings. For example the 6-cell battery found on Acer's netbooks and lower end laptops usually are rated at 4400 mAh. On locally available 11.6-inch Acer TimelineX 1830T, the 6-cell battery is rated at 5800 mAh. The 6-cell battery on the Acer Timeline X 3820T and 4820TG is rated at 6000 mAh.
Basically, when checking out laptop specifications, don't just ask how many cells the battery has, but take a look at the battery itself and check out the mAh rating.