In this condition the only source is the charging system with all of the current coming from R/R(+) and all of that current must return to R/R(-).So grounding the R/(-) to the battery(-) only forces all currents to return via paths that go to the Battery(-) before returning to R/R(-).
You might ask what is wrong with that? From a charging perspective you want to keep the voltage across the R/R and battery identical. Some loses are expected but they can be minimized by only having battery charging currents running between the BAT(-) and R/R(-). You cant quite do that the becuase all current go to R/R(-) but what you can do is create a SPG that is close to the R/R(-) (using a heavy 14awg wire) and then run all grounds to there before jumping on through the heavy 14 AWG wire that is very short. In this situation there is only 4 amps returning from the battery while the other 10 or so amps are returning to the SPG bypassing the battery.
Net result is improved charging becuase the R/R and battery voltages are closer together as can be verified by the Phase A voltage drop testing.
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