The flicking between red and green is normal. They are pulse chargers, so pulse through a 420mah current to the battery before checking voltage and eventually cutoff to end the charge. You will notice the charger stays red, and flickers green intermittently at the beginning of the charge. Then as the batt gets fuller (closer to cutoff) the pulses are shorter and the red/green flicker happens more often until eventually the green light on the charger stays on.