power cut out

Hi. My drone has been working a dream but I haven't flown it for about a month and have just tried powering it up by pressing the button for several seconds but the battery lights just light up and then turn off. Not sure why this is happening as it hasn't happened before. any tips or advice...

Hi, Really really close call this time.. phew!!! was flying over a River, Flat area.. No Transmitter poles etc , Sandy ground and light wind. Calibrated Compass, had 9 satellites and Flew on 2 batteries flawlessly in GPS mode. On the 3rd Battery while flying it back to me it suddenly acts...