You need to start with your power demand measured in watts. Then divide by 12V to derive the amps. Then find the right wire size and fuse to protect that wire. In your case you have stated 100A * 12V = 1,200 watt charger. Verify this is correct.

If your highest demand is 100A, then you will need a 4ga pure copper wire. Your distance is close enough so you will not have any appreciable loss at that distance.

So, the answer is no - your 6ga wire will not support 100A continuous. You will need at least 4 ga.

Best,

-Jay