I have been jumping batteries for more than 60 years,never had any problem with doing it. Did that in the days of metal bumpers, if you had to park behind the car you were jumping and your cables were not long enough to reach you could put your bumper against his and hook your cables together between the hot terminals. Provided the cars had the same ground polarity. If they didn’t you had to either remove both cables from the car that ran or remove the battery before jumping.
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