radio wiring

[dvjoiner]

I would like to wired a radio and amp to a second battery can I wired it like this ?

 

[zman]

Don't think it will read the 12V unless your second battery is grounded the same as your primary one(to the frame) using the ground from your primary battery doesn't count for grounding the secondary, they both need grounded.
You could run the negative from the second battery directly to the radio then it would work.

 

[Ansimp]

If you are wanting to use it as a charging circuit it will work. A better solution would be a VSR ( voltage sensing relay ) so that you don't run the bike battery down when trying to start the bike. The other thing to remember is that you still only have the same charging capacity even though you have an extra battery.