How reliable is the battery data in ubuntu the power statistics?

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http://askubuntu.com – Right now the power statistics show that: Energy when full: 25.5 Wh Energy (design): 93.2 Wh And indeed the battery doesn't seem to be lasting as long as it used too. My question: Is this data reliable? Does it really indicate that I should replace the battery, or could it be the charger, laptop, or OS that is stopping the battery from fully charging? Is any way of validating the battery is indeed to blame? I'd like to be sure before shelling out 90$ for a new battery. (If it helps, the battery is a 3 year old dell 9 cell rated at 90 Wh). (HowTos)