Originally Posted by Cloudrnnr
Looks like the other wrinkle in this is the distance from the current inverter to battery bank (about 8ft). According to Magnum, the 2800w would require doubled 4/0!
Here is a wire sizing calculator: Voltage Drop Calculator - for single and 3 phase ac systems and dc systems
Using the above calculator I come up with a 1.9% voltage drop with 8 feet of 4/0 cable with 230 amps of 12V power. That is for a pair of wires, i.e. a plus and minus pair. 230amps is about the max the inverter would pull.
Personally I prefer 1% max loss, but for the distance 1.9% is not bad.
Another thing to remember is you are very unlikely to pull 230amps very often for very long.
The microwave will pull about 140-150amps of 12V through the inverter. You could be running a coffee maker, toaster, hair drier, etc, at the same time. Again not for a very long time.