Got an e-mail back from a lenovo sales rep this morning with the official specs on each battery for the t61.

Hello,

I received some word back from our brand team on the specs of the batteries for our new T61.

4 cell is 8.14" wide x 1.57" deep / weight is 221 grams / battery life is 3.6hrs with integrated graphics, 2.4 hours with dedicated
6 cell is 8.81" wide x 2.51" deep / weight is 325 grams / battery life is 5.5hrs with integrated graphics, 3.7 hours with dedicated
7 cell is 8.81" wide x 2.51" deep (same as 6) / weight is 386 grams / battery life is 6.4hrs with integrated graphics, 4.3 hours with dedicated

Take care,