I have a Dell Studio 1555 and it's only about a year and a half old. A few months ago a red X showed up on the battery symbol in the BOTTOM CORNER of the screen and a pop up said I should replace my battery. It lasted about 20 minutes without being plugged in. So I got a new battery in January, which only lasted one hour without being charged and it died again last week. Why do my batteries keep dying? Is there a way to FIX this? Thanks!!!
I know it not a fix, but as you can see from the link, a few people are not happy with this battery, you may be one of the 'unlucky' ones!

http://reviews.dell.com/2341/312-0702/dell-dell-85-whr-9-cell-lithium-ion-battery-for-for-studio-15-1537-1555-laptops-reviews/reviews.htm
I  looked at two sites about your laptop.  One that sells it claimed up to 8 hours of battery life.  Another was PC mag, which reviewed it, and which is usually accurate and one of the advantages they listed was long battery life.

When the laptop was new how long did the battery last?

Can you borrow a charger from someone else and try it?  Since you got a new battery and it only lasts a short time, my first GUESS is that there is a PROBLEM with the charger.