Batteries: Two-6V In Series, or Two-12V In Parallel ???

I have to amend my estimate on how much football you can watch on TV vs. the energy used making coffee using a battery/inverter setup. Two pots of coffee equals one football game. I used a Kill-A-Watt meter to come up with that rough estimate. Going back to the original question of 6 or 12 Volt batteries; an unofficial poll I took traveling across country comes out on the side of parallel connection of 12 Volt Batteries. The point that keeps coming up is if one battery fails, it can be taken out of the bank. At at the lake, one camper borrowed one of his four 12Volt batteries to replace his trolling motor battery that suddenly developed an open cell.