I am new to the forum but found out a useful piece of information regarding the Moto G and the battery not charging / not turning on issue that most have dealt with thus far. It seems that when the Moto G battery is drained to 0% the phone may or may not take a charge and turn on from that point. I myself suffered from this and tried a multitude of different things to try and remedy the situation. I tried the power button for 18+ seconds, leaving the phone off for 24 hours, but the one option that wasn't suggested worked like a charm and had my phone up and running within 5 minutes.
The solution? just unplug the battery. Be warned though, that this requires you to take the back of the phone apart and remove the flex cable holding the battery in place. If you unplug it and pop the cable back in and plug the phone in to charge, the status LED should light up and then the phone will start taking a charge. I hope that this helps anybody that is having this issue with this phone.