2nd solar build

[Teddy]

I am looking to connect two 12V 170aH batteries in parallel.

To my understanding in parallel this would yield 12V and 340ah.

To connect the two batteries in parallel how do I figure out what size cable to use?

This system will be able to deliver 34A for 10 hours, 68 Amp for 5 hours.

How do I determine what the maximum current flow in the cables that connect the two batteries will be so as to size the cable?

 

[MisterSandals]

Presumably your batteries will be next to each other and you will wire your loads from + on one battery and - of other battery (aka balanced).
So between batteries for 68A x 1.5 would be plenty.