Grounding to the actual battery itself is even better than ground to the chassis. It gives you a DIRECT path to the battery (and alternator if the big3 is completed).
Unlike when you ground to the chassis, when the reference point of ground in the front... and ground in the rear can differ. There is MUCH more resistance in the chassis itself... current has to travel through the entire body of the vehicle... through shoddy welds... and sometimes piant/undercoat.
Grounding to the battery gives you the EXACT same reference point of ground as the battery itself (power source) AND alternator (again, if you've completed the big three).
Why do you think dBDrag competitors run dozens of runs of positive AND negative to the rear of their vehicle? You think they would do all the negatives if they could just get the equivalent by running a dozen chassis grounds to some point on the body of the car itself in the rear?