i have a hitec x4ac charger that has a fast charge option and i dont understand what it does differently than the balance charge mode. i recently charged 2 of the exact same battery (2s 5000mah 40c). one batter i put on fast charge mode at 5amps and the other battery i put on balance charge mode also at 5 amps. both batteries charged at the exact same rate and finished at the exact same time (about 45 minutes). i watched the the voltages during the charge on both batteries and they were the same for both batteries so i am confused on what fast charge mode does. you guys have any ideas? thanks