Woot offers Duracell 21/23 12V Specialty Alkaline Battery for $2.99 (orig. $19.99). Free shipping for Prime Members.

Product Description:
Duracell 21/23-12V Alkaline-Battery Volt with Long-Lasting Power & Triple Corrosion Protection - For Key Fobs, Car Alarms, GPS Trackers, Radio Devices, Garage Door Openers & More