Once more. The battery determines its state-of-charge by checking the voltage. As the pack runs down the voltage drops. Once you land & remove the load from the battery the voltage recovers. Also the battery cools which means it can't deliver full power. Now you plug the pack in a day or two later. The Phantom reads the now recovered voltage & all looks good. You only have the computer, GPS, cam, & lights running. Small stuff that doesn't draw lots of power. Again everything looks good & you think everything is fine. But when you punch it to lift off the motors immediately demand lots of amps. The battery is now at room temperature so very quickly the voltage drops &, if any cell reaches 3.0 volts, the battery immediately shuts down. Thus your Phantom comes crashing down to Earth.
WHY RISK YOUR PHANTOM??? CHARGE THE DAMNED BATTERIES!!!