How to power a 12V6A peltier device with a 14.4V battery?
I would suggest that you don't use any resistor. The Peltier element can be connected directly to the 14.4 volt battery. 12 volt Peltiers are usually meant to be used in car refrigerators and the car battery runs at 14.4 volts when the car is running. Car and motorcycle batteries work best with the Peltier element, because they can deliver the 6 amperes the element wants to take with no problems.

When discharging lead-acid batteries, note that they suffer (age) if you take more than half of their capacity before charging them again.