David, Here is another way of looking at it.
When the car was built one of the last things fitted whould have been the battery,
The brake lines would have been installed earlier in the build.
So unless new rear brake lines have been installed (incorrectly) with the battery in situ, its the only answer.
Fluid brake lines are small diameter rigid steel tubes. mostly fixed to chassis.
Handbrake cables are semi flexible thicker tubes with flexible Bowden inner cable.
The battery will pass beside the handbrake cable when lowered from above
jack the car up from the centre of the rear cross beam just enough to clear the battery height.
Ensure you use axle stands before you reach underneath.
Unless you have a car lift there is no no need to physically work underneath other than to slide the battery out along the floor at arms length.
Place the new battery in position on the ground, lower the jack and lift battery into the battery tray from the top.
