Rhombus,
If you're willing to forgo some non-essential luxury items, like the cruise control, the alarm horn, fuel lines and the rest of the worthless junk piled up on the right side you can put it next to your other battery! :licker:
For that matter, save some fuel by ripping out the motor and putting an electric golf cart motor and 6 batteries. That way you qualify for a tax break and you now have sufficient power to run ALL the electrical accessories you want! (Just kidding!)
I believe sooner or later with all the accessories being added to our X's, dual batteries will become an issue. I just fixed before it became an issue. Anyone who undertakes a project of this scope, should be a well above average mechanic with a solid background in electrical design and implementation. Not only do you have to make the alternator work, you also have to make the dual batteries run the factory electrical EXACTLY as designed. This requires a great deal of planning and work. It also helps to have access to all kinds of neat electrical connectors. Otherwise it will be a huge mess of wires and if a problem does occur, you will have a tough time finding it if you don't have it set up right.
I can tell you the advantages and disadvantages to my system. First, it does take up some space in the back of the truck. Since I don't use the interior bike rack (Mine stay on the roof), this hasn't been much of an issue. You will lose the interior bike rack in the installation though. You will also have to rework the rear carpet to have access to the rear tie downs. It will also be a little harder to change your tire since the left side battery sits on top of the jack cover. There was no way around that because of the design of the cover.
The great thing about it is the fact that I now have a jump start any time I need it. My system uses a bridgable isolator that with the turn of a knob will jump start the main battery from the auxillary. It also allows me to run my high current draw accessories (lights, compressor, etc) with the confidence of not worrying about if I am wiping out the battery. If I do, I just turn them of until I recharge the battery. I can also get away with running more accessories on my main side for longer since I know in a worst case scenario, I can always jump start it from the aux battery.
Something was brought up to me this weekend by Richard that would hold true if you are winching on a single battery. Somebody told him that if you have the engine off, you will have more current available for winching. That is true, but, there is a caveat. If you have the engine off during winching, you can't provide assistance to the winch through the vehicles driveline. You are doing a dead pull. Yes, the engine will draw current while it is running, but when you consider the increased current necessary for an unassisted pull, the difference is overridden.
With dual batterie isolated, you have the full power of the auxillary battery going to the winch without the engine being a limiting factor. You still have a draw on the alternator, but even at 2,000 rpms, the alternator output on an Xterra is miniscule compared to the current your winch needs to continue operation.
These are all something to think about as you take on a project o this magnitude. It has its good points and bad points. You have to determine if for you, the ends justify the means.