Much like cell phones, the laptop batteries provide less and less max usage time as they get older.  Most manufacturers do not have very good warranty coverage on batteries for exactly that reason, with most lasting only one year.  Buying a replacement laptop battery straight from the manufacturer can be very costly, but there are other options.  Amazon.com has an extensive selection of replacement laptop batteries for nearly all makes an models and provide free shipping on most orders over $35.  They even have prices which are often less than half that of the manufacturer.

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