Laptop batteries are rated by, Voltage (V) and Milliamp-hours (mAh). Voltage
is the rate at which energy is drawn from the battery and Milliamp-hours Represents the capacity of the battery. The Milliamp-hour rating Corresponds to the run time of the battery. A battery with a high Milliamp-hour rating has a relatively longer run time than a battery with a Low Milliamp-hour rating.

Batteries with different Milliamp-hours can be used on the same laptop provided the voltage rating is the same. The voltage rating has to match that of the original battery or as recommended by the computer manual. Using a battery with a different voltage setting can seriously damage the laptop. The power ratings of most compatible/replacment batteries are higher than the original manufacturers' batteries. This will not damage your laptop, in fact, it simply means that these batteries in many cases last longer than original manufacturers' batteries. Ask the experts like
PowerUp on compatible replacement laptop batteries.

The run time of a laptop battery will vary on individual notebook computers, based on the applications being used (i.e. high graphics, games), the number of times something is saved or retrieved from the hard drive and/or CD Rom drive, the memory of notebook, and chemistry and capacity of the battery. A 'realistic' average run-time for a battery is 1.5 to 3 hours. Using devices like a wireless adapter on the laptop also drains the battery considerably.

The life of a battery under normal use is around 500 to 900 charge-discharge cycles. This is about one and a half to three years of battery life for the average user. As the rechargeable battery begins to fail, the running time of the battery begins to decline.