Why is my battery going up and down while charging?

I was charging my phone off of my chrome book and my battery would stop charging because the phone was getting over heated so I took the battery out and let it sit for 5 min and then put it back on charge. Then my phone would say it was over heated then jump my battery to 50% when it was at 2%. Then I would unplug it and it would say 13%. So I put it back on charge and it would do it all over again.