Day 1 Of the Derv-Beast Commuter challenge

[Uberderv]

It's quite straight forward mate. Get y'sen a good sturdy battery box and bolt it down in the boot, reinforce if necessary as you don't want it going airborne in a crash. Buy some thick welding cable, roughly measure out and add maybe 1/1.5m on it because all those twists and turns soon use it up.

Route the cable through the car making sure it's not going to chafe on anything. Purchase a box which you can terminate the cable in, I think they are called a shunt box, this is where you can connect to the original cable without the danger of shorting it.

 Now stick your battery in the new box, secure it down. Remove the original box from under the bonnet making any brackets required to hold the ECU etc..... secure the shunt box and connect the original positive/new cable inside it. Connect the earth to a point on the chassis. Now from your left over cable make an earth lead and attach it to a good point close to the new battery location. Connect the earth up,  connect the positive and away you go

 Fitting some sort of fuse or breaker close to the battery on the positive might be wise too. Hope that helps a bit.