My ZTE ZMax is a great phone but recently, even with the phone battery at 58%, on reboot the battery charge shows 1% and quickly drops to 0% and shuts down. When I plug in charger, the battery display shows 58% and charging.
Sounds like your battery is going bad and is going to need replacing.
It is extremely common for a battery to give a false reading, false percentage of charge amount, when it is going bad. It is because it holds less and less of a charge. While they should say it only has say 5% left or after charging say it only has 5% charge, for some reason they aren't set up that way. Instead they will often say they have a much larger percentage of a charge when they have almost none.
The only resolution is to get the battery replaced.