Where did you get the current readings for the 2 fish detectors? 
If your detector is drawing .75 A then it requires .75AH each hour.  Also .75AH is the same as 750mAH.
The 3 batteries you listed are 8330mAH, 10830mAH, and 15000mAH. They will run your power hog .75A for 11 hour and 6 minutes, 14 hours and 26 minutes, and 20 hours. 
A serious fisherman needs to have a detector working about 7 hours a day so one of those 15000mAH batteries will last about 3 days. So for a 10 day trip you only need 3 of those 12LB batteries.
I am looking at how the current varies with the depth of the water and have found that my detector draws about 2 times as much current at 30 feet as it does at 3 feet.  I should have better data on several detectors in about a week.
You might consider one of these for each day
  (You need to Login or Register They are not stocked in US so shipping charges may be $20 but if shipping several the per item cost may be reasonable.  YOU WILL NEED A PROTECTION BOARD.  I can get you information on those if interested.