2019 Kia Optima, Adding A Second Battery In Trunk?

Brand new here and a novice with adding a battery in the trunk. I have a 2019 kia optima lx with 2 kicker amps one the a 800x1 and another 4 channel 65×4. I wanted to add the xspower 680 in my trunk to help with dimming lights. It is just a little nothing major. I don't quite understand how to install the battery I get run the positive to positive then another one off that second battery. However from there what fuse do I need for that second battery the. From there to fused distribution block?Anth b

Fuse at the 2nd battery , within 12" and the primary battery again within 12" inches. One wire with a fuse ate both ends.

Ok so positive from main battery to fuse holder and fuse to positive of second battery off that to another fuse holder and fuse. Then through that to fused distribution block to amps is that right? One last question for second battery do I use the same size fuse as under hood or will the xspower say what to fuse that battery at?Anth b

In my opinion it is more based on the size wire you're using. 4 gauge I would use 100amp 0 gauge is what I would run and use a 300amp fuse. You're protecting the car in case of damage to the wire.