how to connect to positive battery post

They’re “bedfellows”. I’d go with “A”, it’s less likely to get crusty, and the connection would be undisturbed if you were swapping to a new battery. It looks to be purpose-built for connecting accessories like yours.

 

"B" holds the clamp to the post. "A" is for Main power and accessories....

 

B will set off tiny sparks as you loosen and tighten it. Been there done that, both A and B on mine are used for other connections.

 

Neither one is ideal. If you loosen that clamp and lift it off the battery post, you will notice it drapes down over the side of the battery and contains a 140 amp fuse, and there is another place you can connect—let's call it C—at the bottom end of that fuse.

C, for the win, for two reasons. First, your added wiring is now protected from the battery by the 140 amp fuse. You still need your own fuse sized appropriately for your sub and your added wiring, but the 140 amp 'feeder' fuse helps limit what your added fuse and wiring can be exposed to.

Second, most of the time, as you listen to music with your car in READY, the power isn't coming from the battery, it's coming from the inverter in the front of the car, and connecting at C, you have shortened that path by not having the 140 amp battery fuse in it. (There is still a 125 amp fuse at the front of that cable, protecting the inverter output, so by connecting at C, you have a tap point that is protected that way from both ends.)

It's a little tough to see in this pic because of so much other stuff around, but you can see the solar charger kind of velcro'd on where that fuse hangs down over the side of the battery, and the cable tapping off to the added fuse box is attached at the bottom end there.

Point A is purpose-built to give you a way to change the 140 amp fuse if you have to.

 

We can create an option and not use the given?

Id go with D, buy a battery clamp that has multiple bolts to provide better and safer connections.

D takes the cake and champagne bottle.

 

D is exactly as bad as A and B, for the same reasons.