Precision 3581 empty space near the battery

Hey,

My Precision 3581 came with a 64Wh battery (the smaller one), leaving some space nearby. I heard I can swap it for a 97Wh battery.

Also, I'm wondering if I can add a third SSD. It seems the BIOS supports it, but I can't find any info on how to do it.

Any ideas?

Andrew