I'm buying a Gateway E155-C for school, and have 2 battery options-the standard 6 cell, or upgrading to an 8 cell. Is there a significant weight difference? (It's a tablet PC, so this is reasonably important.) Big battery life difference? Would the 8 cell battery still be completely contained in the laptop, or would it hang out? (I've never owned a laptop, and don't know how the batteries work.) Is it worth $40 to upgrade?