Hi Guys,
I have a 4 things to mention regarding only getting a little toast and a couple cups of coffee from three batteries.
1) The faster you go, the less you have.
One thing to keep in mind is what percentage of your battery bank's capacity are you drawing when these high drain appliances are operating. I've included an excerpt at the bottom of this post from:
http://www.windsun.com/Batteries/Battery_FAQ.htm
(sorry, the table columns won't stay tabbed in this forum)
Bottom line: a 1400watt inverter running at full capacity will be drawing somewhere in the neighborhood of 140+ AMPS from your battery bank (I checked in our kitchen just now and our toaster oven draws 1660 watts and the coffee pot is 825 watts as an example). Also, don't forget to take the inverter inefficiencies into account!
Assuming that your 12V batteries are in the area of 100amp hours each, you are drawing a pretty high percentage of your total capacity. The higher percentage of your total capacity you draw, the more Peukert's Effect has to be taken into consideration. Peukert's Effect can vary quite a bit from one battery model to another so you can't really "take an average" and apply it to your batteries. Poorly made (as opposed to inexpensive) batteries with a high internal resistance will have a more pronounced Peukert's Effect. If you are REALLY interested, you can do a rough calculation yourself by drawing your batteries down at two different known rates and calculate the effective energy provided each time....
Or, if you can find the a manufacturer's data sheet that shows the Peukert's ratio directly, or shows the AH capacities at two or more rates, you can calculate it that way without the Mr. Wizard experiment...
2) Battery Construction.
Batteries that aren't rated in Amp Hours, but use Reserve Capacity instead, >>typically>at least