Why do some X60s weigh more than others

[sparta.rising]

This may have already been covered, I'm usually a T series man, but I'm looking into the X series for someone.

Why is it that the 17043DU weights 3.46lb and the 17044DU weight 3.0? Both are X60s, are similarly equipped, except that that the 17044DU has a fingerprint reader and more ram, wouldnt that like make it heavier?

[sonoma]

The difference is 4-cell battery vs. 8-cell