I would look for replacement cables in an appropriate length, particularly if you're talking about one large positive and one large negative cable. Often appropriate cables are sold as "switch to starter battery cables" and come in various lengths and gauges.
I think West Marine (and probably other stores) will make up custom cables to specification for not too much cash, as well; certainly easier and cheaper than purchasing a decent crimp tool for a single set of cables.
If you have a bunch of wires, you could either extend all of them, or preferably put in some sort of a bus bar or distribution box and run a single set of cables to the battery.
If the new wire run is more than a few inches, it would be a good idea to put a fuse in the positive lead close to the battery to prevent a fire in case it should ever happen to short out somehow.