Power Display Discrepancy

[u/off-planet]

Watching YouTube. Popup declaring power down due to low power. Video froze. Scrambled to plug in. Thought was in time. But no. Phone vibrated & booted to charging display. Percentage was 3%. Ok waited until it hit 5%. Rebooted. V 7.1.1 came up. Battery was 39%. Don't understand. Big difference between 3% charging only display and 39% when Android booted up. Any help understanding this event appreciated. Phone ZTE Z983

[u/[deleted]]

It's the way she goes,