tablet wont accept charge

Hi, I need help my daughter tablet dead & wont accept charge, so I open back cover disconnect the battery & reconnect but no luck, I measure battery voltage 3 volts

next step I did was disconnect battery & direct charging the battery for four hours ( I create modified one with alligator clips so that I can access to the positive & negative of the battery) check battery voltage 3.7, I let it charge for 2 more hours to make at least 4 volts but it stay at 3.7 volts,

I removed the charger and re connect the battery, switch power button on and galaxy tab display but its freeze in this mode and logic board start heating I can feel abnormal heat even in the display screen. I off the unit and did the normal charge & battery icon display but it wont accept charge . the final thing I check was remove battery connection and put the charger in normal way to check if the logic board still heating & its not, check battery voltage to terminal connecting to the battery 4.2 volt

I conclude that when my battery down to 3.2 volts it will totally dead