You can add a second batt with less CCA, or you could just add some ballast high left rear as well. Or you could even go with a smaller Lighter bat and figure your true traction issue out and stop throwing weight at it to fix it.

Without even seeing a launch of your car, I'm guessing the right rear is lifting abit first causing you to spin loosing your 60 ft time. Just a guess really, may not even be close.

Bottom line, no more bats, figure the traction issue out.