How to calculate amp hours when voltage and amperage changes
In order to get an Ah rating, the battery that is being tested has to be drained down to 0 over the course of a specified amount of time.  The amount of amperage that it took to get it down to zero, over that specified amount of time constitutes the Ah rating. I think your battery is 20 Ah, you will need 4 hours with 5 A, 4h*5A=20Ah to discharge your battery. 
you need to consider the load of your multimeter, so if this is in high impedance, 1.1 V it's ok.
Power disipation = V*A = 1.1 V * 5.6 A= 6.16 W