i spent @6 years as a repair shop, warranty and non-warranty; for several brands of fence chargers; not all fence chargers are equal, and you do not always get what you pay for; i did test several battery powered units, and for the money, i would go with a parmac unit. (spelling may be wrong) its parker/mccrory or something like that; the 12volt model has enough output to stop most critters, the 6volt is cheaper, doesn't have as much output, but worked well on cows that had already been trained via a ac powered charger; a friend uses a 6volt to keep critters, including bears, out of his garden and bee hives, he says it works fine..you can pay a lot more and get the High dollar units, but i have access to a lot of chargers, and i use the parmac..
heehaw