Why does my ZTE say its "charging" but battery goes down?

I will plug in my ZTE ZMax Pro and the phone will sence that the phone is "charging" and have the charging symbol, but if I leave the ohone alone to charge the battery will ethier stay the same or go down. I have tried to replace the battery 3 diffrent ones, I tried 4 diffrent chargers, used 3 diffrent charger cubes, plugged into 5 diffrent outlits, and still nothing. Ihave even tried to take apart my phone and blow it off to get the "dust" out of it. For it to charge I usally have to restart my phone 7 or 8 times in a row each time removing my battery. I am getting very frusteraded because it NEVER is fully charged, and my alarms don't go off when my phone is off and charging. I need it fixed soon. Someone please help me!!