I did this and got the group 65, I bought online and found another coupon so search for a coupon code and keep trying all the ones you can find hopefully you'll get a hit on one. Once paid for online they typically don't bother to ring you up for another transaction for a core. Worked for me. Now I have 2 batteries
http://www.sears.com/diehard-platinum-automotive-battery-group-size-65-price/p-02851065000P?prdNo=8
http://www.sears.com/diehard-platinum-automotive-battery-group-size-65-price/p-02851065000P?prdNo=8