I had been flying for around 15 mins on a fully charged battery (second flight) I landed and stopped the motors. Then tried to restart them and found the Phantom was switched off. When I do a test on the battery it shows 3 lights out of 4, also I got no low battery warning lights before landing. Trying to turn the battery I get a very quick flash of the leds and a very short quiet beep. Battery is stock and brand new and firmware was the latest (2.6 ?) Any ideas ?