Interesting issue with my wifi Car project
the nodemcu's 9v battery gets hot in a minute and stops working. What am i doing wrong?


You're using a 9V battery.

Those batteries are useless. They have very little capacity, and can provide very little current. The NodeMCU needs a lot of current. 

Choose a better battery. Maybe a Li-Poly battery would be good (mobile phone batteries are good for this).