Hi. I just opened took out my phantom 2 that I have not been using during winter. battery had 2 leds so I thought I would boot it up and upgrade firmware. it just quickly blinks then nothing, no sound or anything. pressing the battery button for a few more seconds all leds light up but still no life whatsoever in the phantom itself. it worked perfectly when I last used it, battery has not been inside the phantom during storage in winter. any thoughts?