Be cautious installing it, but yeah, it's can either go in place of a battery, or parallel with a battery. If you are putting it in parallel, you need to pre-charge the capacitor. Look around for car audio capacitor install guides to show you how to do that. It sounds like you are using it as a replacement though, so it shouldn't be an issue.
The company should have some kind of install guide as well if you email them. Good luck!