2007 Grand Prix starting issues

we added another body ground wire from the battery to the inner fender well under the fuse box since that one was pretty rusted. we also had the battery voltage checked at 2 different places which showed it was working fine. after the ground wire was added the only issue we had was a slow start which would still pop the trunk. we decided to replace the battery and with that we no longer have any problems. all symptoms are gone. Bad body ground, and a battery was the problem.