I've owned several laptops in my life -- and I love them. But as most photographers who use laptops know, they can behave unpredictably on occasion. My current laptop, a Dell Inspiron E1505, is about a year and a half old and is starting to show signs of battery fatigue. The battery, when new, would last about 4 hours on a full charge. Currently I get about 90 minutes or so out of a battery charge. There are a number of things that can accelerate a laptop battery losing it's charge sooner than expected:

-- use of wireless internet or device connections
-- powering external peripherals such as hard drives, flash / pen / jump drives, iPods, etc.
-- screen brightness

All of these factors seem to be things that a photographer would and could expect to do with a laptop. Most often I have an external hard drive AND my iPod connected to my laptop while connecting to a wireless network...so I've certainly put the battery through it's paces!

If you find yourself needing to replace a laptop battery, you should do two things.

1.) research online for consumer reviews of various battery options (name brand vs. "knock-off", extended cell vs. normal cell, etc.)
2.) properly dispose of the spent battery through an approved battery recycler (you can NOT just throw them in the trash due to environmental restrictions!)