Thanks for all your help.
Here is what I did to fix it.
1) Tight the nuts on all battery connections
2) instead of push one end to start the generator, push other end for 10 second, I started to see red light on the power indicator, then push to start generator again. and that DID started the generator
3) Tight the 50 amps electric connections , because I park far from the house receptacle, the wire was really stretched. one end connect to RV is not tight enough, so it did pass some electricity to power the RV inverter, but no enough power to power the 110v!!!
ALMOST HAD A HEARTATTACK!!!
