Unlike cars, there are no standardized tests for laptop battery run time. Laptop manufacturers can use any test methodology that they want so results are usually unrealistic, overstated, and always carry a lengthy disclaimer to say that they may be completely inaccurate. Without a reliable source for battery run time data a battery supplier can only supply an educated guess.
The best way to estimate run time is to compare battery ratings with our own experience. This method will be the most accurate because your experience will reflect your individual computer configuration and usage patterns. A replacement battery with the same watt-hour rating will produce the same run times as you experienced when your old battery was new. If the new battery has different ratings, the difference in run time will be directly proportional to the difference in capacity. You can use this information to make an educated guess about the run time of a replacement battery.
Estimating Run Times Based Upon Power Consumption & Battery Capacity
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Using this chart you can estimate the run time of a different battery. For example if your current battery is a 48Wh 6-cell battery and ran for about 2 hours when it was brand new then your average power consumption is close to 25W. If you follow the 25W line to the right you will see that a 74Wh 9-cell battery will give you about 2.96 hours and a 97Wh 12-cell battery will give you about 3.88 hours. This is only a ballpark estimate and the accuracy is dependent upon your actual average power consumption and the actual ratings of the replacement battery. Note that the watt-hour ratings are representative of common battery configurations and will not match all batteries with the same number of cells.
