Adding dual battery - how to ground?

I am planning on adding another battery so I have a dual battery setup, to handle a stereo upgrade. I think I have most of it figured out, but not sure how or where to ground the new second battery. Currently there is a very thick ground cable that looks to run back to the engine, I am guessing there must be a way I can use that somehow to ground the new battery.
Any suggestions or pictures would be great.
This is on a 2013 LSV.

This is how I set mine. Picture is from another member and not my original work!Attachment 25567

You will need to ground the new battery the same way, you need to either tie it to the other battery or ground it to the block.

Connect it to the other battery.

Perfect, that is the information I was looking for. Thanks!