"someone told me (probably incorrectly) that the more stuff you had on your memory, the shorter the battery life... I guess you're saying that's not the case."
I think there's just a bit of a muddle overterms.
"Memory" refers to your computers memory, and it won't be 140gb and more than likely less than 4gb.
The 140Gb will be your computer's hard disk drive.
Memory is for temporary storage used when your computer runs stuff.
The Hard Disk is used to store things and they stay there when the machine is turned off.
So does more stuff in memory shorten battery life?
Well a little bit yes. Running lots of programs at once, which take up memory once they're loaded from the disk, will for technical reasons cause your computer to get through it's battery quicker.
Does more stuff on the hark disk drive shorten battery life?
No, not really, perhaps a teeny tiny bit for very technical reasons but not anything worth worrying about.