-Run the power wire on the passenger side via the huge ecu grommet into the car. Take off the door sill on passenger side, tuck the power wire under the carpet, run it along the passenger side under the rear interior 1/4 panel cover then into the trunk.
-Route the wire to the passenger side rear area behind the tail light.
-Get a 100amp circuit breaker for the 12v power. Or you can use a fuse if you want.
-What ever you use to ground make sure you sand down the metal so you have a good connection. If you want to run more than 1 you can. I've seen plenty of people use shock tower, spare tire area, and the trunk floor near where you can mount the battery.
-Mount the battery on the passenger side rear behind the tail light.
-I would suggest a battery tray with tie down and mount into the trunk
-I also suggest a optima battery or similar drycell
-Have some nice new battery terminals on hand (order from ebay or from car audio shop)
-Make sure you have good ring terminals for your ground and attach them to chassis
-Attach your power wire to the positive battery terminal and wrap it up with electrical tape. (or you can spend more and run a distribution block and run new power wires to starter fuse box etc)
Its not that hard. There are TONS of pictures online that you should be able to figure out what to do, Its not rocket science. There are alot of write ups for the s-chassis, yea not all are super great in detail hold your hand with pictures of every step but you can also look at other car relocation write ups for other cars. Concept is the all same and any person should be able to figure it out pretty quickly.
Here is a good picture of where the battery should go and a really clean job
http://imageshack.us/a/img90/1048/jd...rld240sx22.jpg
http://imageshack.us/a/img705/8383/j...rld240sx23.jpg