This is what Rayovac wrote on their Facebook wall:
October is Fire Prevention Month! We want to make sure your family stays safe by offering coupons for FREE 9V batteries to change out in your smoke alarms. Stay tuned for more information, they will go fast!
As I am writing this the offer isn’t live yet but I would recommend that you keep checking their Facebook page for updates. There is a coupon tab at the top so keep checking that as well.