Please confirm that the item you highlighted is a rigid brake line. It looks like a flexible handbrake cable.
Whilst Morgan’s vary a lot I have never heard of having to disconnect a brake line to fit a battery. It is not an original battery, even if it was oversize it would still need to be fitted, can’t imagine a battery fitter undoing brake lines.
The battery is lowered to the ground from the top, then jack up the rear to slide battery out.
Consider that the battery was fitted from underneath, probably on a car ramp and terminals connected from the top.
