It sounds like you're looking for a coupling to connect two pieces of battery wire. They're not hard to find; you can probably get them at your local auto parts store or online at sites like Amazon. Here's the sort of thing I'm thinking of.
That little kit is available on Amazon here.
Amazon.com: Linkstyle 4PCS 4 Gauge Wire Splice Connectors, 4 Gauge Battery Cable Coupler Audio Wire Butt Connectors, with Wrenches and Screws : Electronics
This gives you an idea of what you have to do; cut both wires, strip the ends, insert the bare wire into the coupler and tighten the screws. The heat shrink tubing is needed for the positive battery wire; it's up to you whether you want to do it for the negative, but it will help keep out water and corrosion.
If you have some extra wire available that will still reach the battery, you can simply cut off the old terminal and clamp on a replacement like this one.
These are, again, readily available at any auto parts or hardware store; here's the Amazon link for that picture.
Amazon.com: ACDelco Gold 3BA35 (88860321) Battery Cable Terminal : Automotive
Again, you'll need wire cutters that can handle battery cable and either a set of wire strippers or in a pinch you can strip the insulation with a utility knife if you're careful. Just cut off the old end, then clamp this on the stripped bare section of wire and you're all set.
Keep in mind that the positive and negative terminals are different sizes, so you need to use the terminal that's correct for the one you want to replace.