Some have had difficulty with car starts because of oxidation or just plain dirt on the few places where the engine etc. is grounded.The dirt impedes whatever electrical flow there needs to be.

There is a large set of these "grounds" right in front of the battery tray.

I took those all off and cleaned them(the little plugs and the base they plug into), as well as the few other places the engine is connected by ground wires to the car frame. That was not my car's problem unfortunately. But is was an easy thing to try. Sorry if the language was confusing.