1. please invest in a new battery. any battery over 2-3 years old will be suffering from "sulphated" plates, which will short out some of the cells which will result in a much decreased amp hour rating.
2. you don't specify aircraft type but it seems it is not a fuel injected engine....so i suggest prime once, throttle slightly open, turn over, if no start then prime again and it should go on the second attempt. if it attempts to start open the throttle and keep the starter turning it may well fire up!