Dell Inspiron 8000 Bios Upgrade Problems

I recently purchase two Dell batteries for my Inspiron 8000. They came with a Bios Upgrade CD (dated April 2007) since apparently the batteries have changed since the laptop was originally purchased. I followed the directions to reset the boot sequence so that it starts up off of the CD, and all goes well when I select update Bios. But in the next screen when I select Inspiron, the upgrade hangs and nothing further occurs. I can back out of all of this and get it to restart and act as usual, but must use the laptop with AC power only. The laptop is running XP Service Pack 2. Must I do the upgrade, or can I just plug in the new batteries? Help!!!!