my car fails to start. My car needs the help of another battery to start every times i wanted to start it. even with a new battery. after i got it started, i shut it off and wait for few minutes and start it normally, it fails. then, i use another battery to help then it got started. then i shut it off again and wait for a few minutes and try to normal start it, it fails too. (evertime my car started, it can go like a normal no problem car, no CEL either. but everytime i shut it off, and when u wanted to start it , i cant perform normal start. i have to use the help of another battery to start)

so, i checked my spark plugs, cables it has no prob. asked if it is a flooding, my mechanic says no. he even checked the fuel pumps,alternator,starter,coils and everything's normal.
check using a computer and no fault code.

guys, can u tell me what could be the major factor??..iam totally lost..it's weird.