The most modern and effective chargers are low impedance energizers developed in New Zealand in the 1960's. Low Impedance Energizers have stronger pulses at shorter duration's using less electricity and working over longer distances than older style energizers. Not rated in Joules, nor rated in voltage against Ohms. Some are not safe to use and are not UL rated.
Most problems involve poor grounding or improper grounding of energizers.
Drive one to three grounding six to eight feet apart the rod must be in moisture to act effectively at all times. The more powerful the energizer the more grounding rods necessary. Do not make up a home energizer or use a continuos power energizer. Do not charge barbed wire as it can create an unsafe condition - get caught and not be able to get away from the energizer. Use a voltmeter to check the fence line.