Pull the welding cable from ur boot to ur engine bay, through the firewall (if not mistaken im share the hole for aircond...).
Connect battery +ve point to ur +ve car wiring, battery -ve point to ur car body at the boot compartment is enough.
Becarefull of the +ve terminal, warp it so that it wont touching to ur car body. -ve is no problem....
Warp the welding cable with thick rubber hose so that it wont scrach the cable at the point its thru the firewall, its happen to me when the cable was cut and touching the body, its like a very bad jerking at that problem, realize its when service the aircond. Thanks god it not burn my ecu.
Use good welding cable.. dont use thin one...