Get the X2 31 AGM battery from Batteries Plus and not worry about it again. That battery is well within Mercurys specs for the Optimax engine and has plenty of reserve capacity as well compared to other 31 series batteries. Id also check your battery connections and alternator to make sure its charging when you are running on plane. Normally you should see 13 volts when running above 2000 rpms. Regarding your poor hole shot as the day goes on, its air temp related as temp goes up, air gets thinner (density goes down since warmer air is less dense). Also warmer air contains more water vapor, which also displaces oxygen further limiting power. Therefore, you have an instant horsepower loss.
