What wire to use for batteries...

2/0 cable, per set of two batteries If you have three use two cables or one 1/0. I prefer using 2/0 and solder the conecsions. Crimping, to me is a problem looking for a place to happen. Running extra ground cables frame to engine on the right side is also a good idea.
If you have a multimeter check grounds extras to the cab works wonders.

 

4/0 For Batteries and Starters and here is why. The Bigger the gauge the Less Resistance to flow that plus if it is a Centry with the Batteries back inbetween the Frame Rails you will need it for the Length of run you will have to prevent a Voltage Drop.

 

Excellent advice from both previous responses. I am overkill on my electrics. I use 2/0 between batts and two of the three grounds(One ground to motor, one to frame and 1/0 to cab) . I use 4/0 to starter. Excessive, i know but i think it is worth the money and pain running it through truck(the stuff is brutally thick). And as John said, solder connectors!
One thing i firmly believe in and didnt see mentioned... Use adhesive heat shrink to seal connections. I use both red and black to quickly indentify connections. And it makes for a very neat and professional looking job and helps prevent electric problems down the road imo...

 

I agree with 4/0 for main cables to starter, 2/0 for battery to battery jumpers.

 

You do realise that 4/0 is small cable used for gas motors.
Battery cabble is bigger the smaller the number.
Welding cable is not good for use as battery cable.

 

Refers to the copper conductor size, according to the American Wire
Gauge, based on the conductor's circular mil area. Gauge numbers
decrease as wire size increases, e.g. #8 is smaller than #6, etc.

 

i had some cables made by this guy, imo the best you can find at reasonable prices

wire gauge chart

http://custombatterycables.com/technical_data.htm

what size to use


http://custombatterycables.com/what_size_cable_do_you_need.htm