I recently replaced my battery in my 2004 Infiniti G35 6MT and found the lack of instructions annoying so I am posting the steps I took to replace the battery. I hope this helps others that either don’t live next to an Infiniti dealer or just want to do it themselves (I fall into both categories). Any image can be clicked on the get a larger version.
Remove the rubber lining around the battery cover that is closest to the windshield
Remove the pins from the battery cover using a flathead screw driver. These should pop out rather easily. There should be 5 that you have to remove.
Remove the battery terminals from the battery using either a wrench or a socket. The negative cord should be easy to move out of the way, but the positive cord was a little tougher since it had some extra hardware on it.
Unplug the two plugs from the bottom of the positive cord in order to maneuver it out of the way a little better. Using a flatehead screwdriver push in on the little bracket that is holding each plug in place.
Unbolt the crossbar holding the battery in place. I only unbolted the end that is clearly visible and then unhooked the other end by twisting it around until it came unhooked.
Remove the battery. This can be tricky since there is very little clearance. You may need to bend the plastic covering a little in order to have enough room to get it out.
Now that you have the battery out, you should be able to reverse the steps to put everything back together. Back in step 1 when you are replacing the pins, make sure to slide the pin up a little before pressing it into the hole. The image below should help out.
After I got everything hooked back up I fired up the car and I was back on the road.