so how to do it? just get wire that extends that long?

You could, but you sould jsut ground everything to the chassis in the case of a rear mounted battery.

u mean bypass putting anything on the battery? i don't quite get wat u mean :)

mebe a drawn picture? i'm a visual person haha

He is saying you won't have to run a ground wire all the way up to the engine bay. You can just ground to the Chassis because that is the ground anyway. However you will still have to run a positive wire. Which you will have to run all the way but to where the battery is now and reconnect to all the wiring up there. And make sure to get one that is thick enough. You don't want to go with a light guage because all the power running through there will heat it up or possibly burn it out. Good luck.