Inverter Problem: Can't Handle Load But.. Should

driver has it right. If you read the manual on any big inverter, it will tell you not to use feed cables more than 6 ft. Preferably 4 feet and under. The connection terminals limits the gauge wire you can use. The correct wire will be the same size of the connection hole. What's happening is you are suffering a voltage drop when the inverter is put under load. Of course you could use bigger cables, but your connections don't allow it. Position the inverter inside as close as you can to the batteries and shorten the feed cables. Then use an extension cord of the right length to get to the microwave. A 700 watt microwave needs about 1200 watts to start and then drops to 700. Make sure you protect through floor holes with grommets or sealant so the wire don't wear through and short. That's where fires happen.

 

If you head over to a welding supply shop you can get some 0 gauge, high quality cables with ends relatively inexpensively. You can even get high quality connectors put on after they cut you the cable.

 

That's what I would suggest. Except I purchased my 0 GA wire at Home Depot, really reasonable.
Here is a Thread I started almost 2 years ago that deals with installing an inverter.

http://www.thetruckersreport.com/tr...313-installing-a-power-inverter-pictures.html