Don't need a deep cycle
Pat, not sure what your battery set up is. If you have a diesel, you should have 2 battery banks so you are not stranded if your battery dies. You probably already do.You can use deep cycles for starting, as Steve says. You do not need a deep cycle as your starting battery, however, and it might not even be the best choice (deep cycles takes longer to recharge and cannot deliver as many amps.). My house batteries are deepcycle, I use them for everything. My starting battery is a regular cycle battery, which I treat as an emergency battery. I don't use it at all, except to test and top off a charge every now and then.