New battery cable

Im going to replace the old cables and my question is what size should i use a 2 or 1 awg cable .The battery is in the trunk and i measured the old cable and it is 20 foot long,positive cable that is and im wondering about voltage/amp loss. I understand the whole voltage and amp process with A/C current but not with D/C especially with high cranking amps in batterys.Also has anyone tried moving the voltage regulator to shorting the cable in such a situation.

Thanks for the info that might be the main cause off the dreaded hot starts i have now.I bought 2 awg for the power cable at 2 bucks a foot but im gonna go with what you suggested with the ground and hope it holds up for awhile. I didnt mention in the before post about almost catching the car on fire somehow the pos cable hit the headers and you can guess what happened.probably from jacking the motor up to replace a locked up oil pump boy did that suck but lucky me got a bud with a garage with a few lifts so he let me borrow one .Beats laying on the ground.