The Speedrite 3000 energizer is rated for up to 120 acres and has a 6 position adjustable pulse speed switch.
Features:
 
Day/night sensor
Easily mounts on wall, fence post, or fence wire
Suitable for multiple types of livestock
Key parts are repairable/replaceable unlike cheaper energizers
Includes power cord, battery lead set and fence lead set
Specifications:
 
Suitable for up to 120 + acres / 48 + hectares
Power source: 110 volt, 12 V battery or solar panel
Max Energy Output: 3J
Power Consumption: 98 mA (fast pulse) or 60 mA (slow pulse)
Max Stored Energy: 1.4J