You may have already heard about this on the news, but Dell has issued a recall for defective batteries in a number of different laptop models. To see if your battery is a candidate for recall and replcement through Dell, visit the webpage they set up for this purpose here:
http://www.dellbatteryprogram.com/Default.aspx

If you discover that your battery needs to be replaced, please follow their instructions on doing so and do not use the battery in the meantime.