I am installing a 2500 watt pure sine wave inverter in my Ram Promaster 3500. I am using 2 12v AGM batteries connected in parallel for power. The power cables will be about 5'. I am running a 1500 watt microwave/convection oven on the inverter. I will be using 2/0 copper cable. Can I ground the battery to the chassis with the 2/0 cable in addition to the existing ground cable? The 2/0 ground cable could be 18" whereas the existing 1AWG ground cable is 6' and has numerous other cables grounded at the same terminal on the chassis. Should I solder or crimp the lugs on the cables? Thanks for adding some expertise to my project!

 

Think of it like this. Whatever is going to come out of those batteries, the cables have to be able to handle that amount of current. So if you run your inverter ground cable to the frame, maxed out it can hit close to 200 amps. That means you need a cable going to the battery negative post from the frame that will handle that much current. There must also be a cable that goes from the battery negative post to the frame, to handle all of the other requirements of the vehicle, engine etc.
The best bet if you are going to run the inverter to the frame, is to run a cable from frame to battery negative post that will carry the requirements of everything. Refer to an AWG chart for length and amount of current. For example, if you are going to run 300 amps from frame to battery negative post, less than 4 feet, 2 ga is going to be more than enough. The frame of the vehicle will handle a lot of current.
Keep in mind that every connection you make to the frame, is now a potential resistance point. Less connections the better.