Plug your Nexus 7 into its original ASUS power adapter using the charger’s original USB cable for sixty (60) minutes. Be sure that the power cord is securely connected to the Nexus 7 tablet and the power adapter.
After the elapsed time, disconnect the charging cable from your device. Within 10 seconds of disconnecting the cable, quickly connect the cable again.
Press and hold the power button for at least 15 seconds to see if the device powers on. If your Nexus 7 does not begin to charge or power on after following the steps listed above, try charging your device overnight, after you check to see if you’re using a functioning power outlet.
One one occasion, the above tips did not work. It took removing the rear cover and the battery cable for 10 minutes then reconnecting and charge up for an hour. It seems the cold temperatures affected the battery and opening the unit made the tablet interior reach room temperature faster.
I hope these troubleshooting steps helped to restore the Nexus 7 battery icon and recharge your device.