Syma X5HW Flight Problem

Hi. I am having a very weird problem with my Syma X5HW quadcopter. As soon as I fly it up, it starts flashing slow as if battery is low even though I fully charged and tested my battery. Battery is fine. When I plug in the battery for charging, it shows that the battery is fully charged. Kindly help me out if the problem is with the quadcopter chipset or battery? Thanks