I was running an electric outboard for fishing. I had a lead acid 12v 85Ah deep cycle battery. I did consistent journeys to my fishing spot, and the battery consistently discharged by 10-12%, i.e 100%-89%, 65%-55%. Am I correct in thinking that I am using approximately 10% of 85ah, being 8.4Ah? If this is so, could I in theory run the same trip off of a Lithium battery 12v 30Ah or am I way off the mark?