Forcefield B30 Battery Fencer 
The Forcefield B30 fencer has a built in smart function that detects when an animal has come into contact with the fence line, then boosts the voltage to maximise the shock.
Once the animal has moved away from the fence line the voltage drops back again and as a result uses less energy than traditional fencers so the battery lasts longer.
The B30 fencer is powered by either a 9V or 12V battery, suitable for 2.25km of fence line or the perimeter of 6 acres.
It comes with a 3 year warranty and free 9V battery, earth bar and output leads.