T&T: amp hour load and voltage drop

[John Holbrook]

My boat has a house battery bank for 3 x 200ah ACDelco Voyager batteries, total 600ah. After charging the batteries and then leaving them for 30min without being charged and no load they showed 12.6V. 
   
  Placing a 30amp load on the batteries for 15min sees the voltage drop to 12.35V. When the lights are turned off the batteries return to 12.55V. 
   
  The reason why i ask is that i have a domestic fridge with an invertor. It general takes 30amps to start the fridge. If the batteries are 50% charged and showing circa 12.2V starting the fridge drops the voltage to under 12.0V and the invertor cuts out.  
   
  Does all this sound normal? 
   
  Thanks
  John
   

 
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