When the battery-low notification appears, I plug in the standard Vizio charger. Unfortunately, it doesn't appear that the tablet can run from the charger only. I'm familiar with the condition of letting the battery get so low it won't boot up, but this is a situation where it seems it doesn't matter what the charge level is, the tablet continues to discharge slowly even when on external power. This occurs in Airplane mode w/wifi enabled. I'm used to running laptops with no batteries at all. Is the USB charging spec less than the Vtab requires to function?