I just did a change over from two 8D 12V batteries on my Monaco Dynasty to 4 6V deep cycle batteries and have had much better power with my inverter. The 4 6V batteries weigh less than the two 8D's by about 30lbs. And was less expensive to buy than the two 8D's. And keep in mind that there is no real 8D 12V deep cycle battery made. And that is from two battery vendors I was working with. They will tell you there is but even the 8D gel or mat batteries are not deep cycle. And by deep cycle they will not take being discharged and then recharged as will a deep cycle 6V battery. So my suggestion is to maybe drop from 6 6V batteries to 4 6V batteries wired in a series, parallel. That way if you do need to use the inverter for any extended period of time you will have the reserve power to do so. On another note my brother just changed his RV from two 12 V batteries to 2 6V batteries and has noticed that he has more reserve power now and he and his wife both use their CPat machines on 12 volt all night. I hope this helps you make a decision as to what is best for your situation.
Larry
PS I bought my 6V deep cycle batteries from Costco and they were 89.99 each. The 8D 12V would have cost me just over 700.00 for two. In the ten years I have owned my coach I have replaced the 8D's twice, this time I refused to, because they do not last as long as the 6V deep cycle batteries. And I also installed a watering system that I can fill all the batteries at one time from a squeeze bulb and hose in a one gallon distilled water bottle.
