Originally Posted by mathteacherrob
Why would you want to install two batteries?? Is there an advantage to this setup?
A winch is a very high drain device, particularly a large one say 12K or more, so it is desireable to have a second battery to help handle the load in the event you cannot run the engine throughout the recovery.
Probably not necessary if you don't wheel seriously, but the other benefit is that you can isolate the batteries so that one runs only the winch and accessories (like trail lights or compressors and inverters), and the second remains charged for starting. They would both charge automatically off the alternator, but only one could be drained by each side of the system. It permits an on-board jump from the secondary as well in the event you leave the lights on, etc.
I second the optima solution because they have a smaller footprint and tend to fit fine if you change the orientation of them in the tray, but whether or not you choose to buy optimas, a deep cycle is the way to go for any serious winching. If you are going to isolate them, a red and yellow top on the drivetrain/accessories respectively is also a popular option. Best of both worlds.