The first attempt to jump start was with the battery in place and prior to discovering the battery was toast. Most cars will jump start across a dead battery.
The second attempt was after the battery was removed. The jumper cables were attached directly to the 9-4X battery cables from a running 9-5. Again, most cars will jump start from another running vehicle. There's more than 12-volts across the posts, so why not?
I bought a new battery, charged it overnight and saw 14.5 volts across the posts. The 9-4X started immediately.