Charger to Battery Wire

[Collin41]

I would like to make some longer wires to go from the charger to the batteries. I h.ave the banana plugs and the battery connectors, just need the wire, black and red are preferred.
What size wire do I need and do any of you have a source?

Thanks in advance!

 

[WHITE-TRASH]

Dean's 12 gauge works good for me.