If I interpret his math, he's saying that 200 amp hours x 3 pairs of batteries is 600 amp hours. At 12v, 600 amp hours - 12v X 600ah = 7200 watt hours, half of that is 3600 watt hours or 3.6 thousand watt hours hence 3 something KWH?
With two sets of batteries that total 400 amp hours and assuming that you only use them to 50% of capacity before charging
, you should treat them as a single
bank. That is keep the battery
switch on all ... all the time. Ideally your engine
starting battery is separate from this 'house bank'. The reason you want to use them as a single
bank has to do with Peukert's Law and discharge rates. Basically 400 amp hours of battery will discharge slower than two 200 amp hour batteries. Without going through the math, it probably goes something like this; if one 200 amp hour battery discharges to 50% of capacity in 4 hours and therefore two would last 8 hours then the 400 amp bank might make it 8.6 hours assuming the same load.
"Peukert's law describes an exponential relationship between the discharge current
(normalized to some base rated current) and delivered capacity (normalized to the rated capacity), over some specified range of discharge currents." (Wikipedia) Peukert constants vary depending on battery type too.
From Wikipedia here's a spreadsheet that illustrates the effect http://www.smartgauge.co.uk/calcs/peukert.xls