Most likely, the copper itself is still in good condition.
Were it me, I would trot over to Harbor Freight and buy a few packages of their shrink-tube assortments = five four-foot pieces 1/4, 3/8, 1/2, 3/4, and inch size.
Clean the old covering as best as possible; pull the splits together as much as possible and hold them together with tightly/neatly wrapped black-tape; then, put two or three layers of the shrink-tube --- one layer at a time of course --- over the entire length.
Split away the old lead terminals with a hack-saw before beginning this repair, retaining as much cable length as possible.
There is absolutely nothing gained by retaining the poor factory design of that mid-cable HOT terminal.
Make that HOT cable into TWO separate cables, WITH COPPER LUGS --- not lead clamps ---, and either connect them to the battery-post via the bolt on
a military battery-clamp, a marine adapter, or a stud-top Group-31 battery.