[xelasnave]

So I had it right more or less. I could not work out how it was 42 amps at 12vlt.
As to price thats not bad. Little things like leads connections etc that take it past a straight battery purchase.
I use 100 amp and another smaller which I dont know its rating but maybe 70 amps and the lap top drains one battery in about five hoirs ...well the inverter shuts down and that is good enough for me. I run the mount only off the 100 amp hour which wont draw it down to far. Recharge next day with a neat 120 watt panel ...which although seemingly expensive had little features that you often have to add like regulator good leads with good bulldog clips or terminal ending..with good fittungs to connect I cant remember but its the best one...all those little things you will need but cost heaps...and stand and good bag...I try to be very gentle with batteries 10 % is my goal discharge.
If I get a cooled camera I will get maybe 150 amp hour just for it...thats big so probably two 75 ah ...you can never have too many batteries.
Alex