No that would be 24 volts. negative to negative positive to positive is parallel.
for 12 volts.You could put batteries in series and use one for 12 volts.
It would really help if you explained in more detail what you want to accomplish! Do you want one battery for starting and the second as a backup? Do you want both batteries on-line all the time? Do you want one battery for starting and the second for a trolling motor and accessories. All of these options have many different wiring possibilities.