how hard is this? i have stupid cheap *** closed end wrenches here at school and it stripped the **** out of the nut on the negative battery cable.

 

You shouldn't need to replace the cable, just the bolt.

 

+1 any parts store will have them.

 

You could also look at a stereo shop. They usually sell post adapters that use a slightly lager bolt head that makes them easier to work with imo.

 

Got a set of 18mm ones with my Racetronix kit
They're a lot easier to get a grip on and resist stripping.

Remember to always install positive first, then ground.
That way you don't risk shorting the positive against the AC line LOL