Probably easier and safer to just replace the cable. 

 maybe safer but definitely not easier, i just looked at the service manual to replace the positive and negative cable harness lol, ouch. 

 Damn. Godspeed ser… 

 If you have enough slack in the cable to still reach after, I'd cut and recrimp the negative lead 

 Shortening the cable and re-crimping it might be the quickest solution, you can also try removing the oxidation on the cable first to see if that fixes it, that green part might be stopping the conduction 

 Depends on a few things.

1. How far back does the damage go. (You'll have to open the harness and find out where the cable is still flexible by hand. A visual inspection won't be enough)

2. Is there enough slack in the cable to reach. (After performing step 1)

There are splice cables and terminal assemblies available if it doesn't reach.

Using a design that solders to the existing cable is preferable, but crimping and using marine grade shrink tubing is second best. 

 Thanks, I cut it back a bit more and damage is isolated to the first few inches, easy to cut and repair 

 Excellent!
Where i am, a little corrosion/high resistance causes damage further down the cable pretty quickly.