Originally Posted by camaraderie
I don't think this is going to work out for you. You have 2... 50 amp hour batts. for 100 amp hours total. Maximum outflow current is about 25% for a wet cell battery or in your case 25 amps..and AGM's can deliver about twice that or 50 DC amps of current without overheating...even with NO losses in wiring & conversion...that is about 600 watts. Way less than you need to brew. Run the genny!
I won't go so far as to say that it's not going to work out but it does put a very high amperage load up on your batteries whenever you activate something with a heating element in it. In the old tt we had 3 group24 batteries. In perfect conditions that man 210 amps and since we never want to draw the batteries down more than 50% I had 105 amps available. We ran a Samlex brand light-duty 2000 watt pure sine wave inverter. It was used for five or six minutes of running the hair dryer(maybe 20) and occasionally cooked a TV dinner in the 1100 watt microwave. Mostly we ran everything in the coach except the converter charger so that we could use all of the outlets in the house to plug in cell phones laptops cameras Etc. We had 200 watts of solar on the roof keeping those batteries charged and sometimes that inverter pull the batteries down so much that I was afraid to turn on my Direct TV late at night for fear of pulling the batteries down too far comma after my wife get one of those 20 minute hair drying things
I don't know what those little instant coffee makers use but I'm assuming it's 12 or 1500 watts and for how many minutes I don't know. I would say if it's going to put a thousand or more watts load on the system for more than 10 minutes to brew a quick cup of coffee you're better off getting a percolator
That's just my opinion and that's the opinion of a fairly conservative guy who takes good care of his mechanical things I know that others draw other batteries down until the inverter shuts off and they do infinite damage to their batteries. Your battery is your choice.
I'm not familiar with the Mercedes Benz charging system but I know with a towed vehicle, the towing vehicle does not put very much charge into the RV batteries and and would never replace the charge that a high amperage inverter takes out in 10 or 20 minutes.
I think you are smart to wire just one outlet and that makes your inverter usage much easier to control. Just try to remember that 1200 watts 120 volts is 10 amps amp 120 volt current usage. That will be more like 110 220 amp draw on your batteries. That means heavy cables to the inverter. Short run from the batteries to the inverter. So try it and in the worst-case scenario plan on destroying your batteries before you learn the limits. Good luck and remember you can get a nice stainless steel percolator online for about $45