I have 40 acres divided up in five acre paddocks, about twelve thousand feet of wire. Had a Gallager S50 with 1.5 joules of power, and paid near$300 dollars for it. Worked great until the grass started touching the fence, then lost too much power and ended up with three chargers on it. This year I bought a Taylor made Brute charger with 6 joules for $399. Have about 7500 volts on the fence right now, so I think maybe it'll be ok. Still some grass to grow up on it. Just watch the price and the joules you get for your money. You can always expand your fence with enough charger, but you can't make the charger do more output. Right now I have a car battery on it, and change it every two weeks. The solar panel for it was another 400 dollars, and I'll get it next year if I'm satisfied with the performance. gs
I have a Parmak and it's the toughest dang fence charger I ever had. Twice in the last three years the nails holding it to the fence post have pulled out and I found the fencer laying on the ground covered in Fire Ants. Washed it off, charged the battery and its still going.
I've started using Parmark or similar 12v charger with any decent battery and a separate solar panel that can be moved to other locations to charge their battery. Have one that has been running since early spring off a lawn mower battery and small Harbor Freight solar panel. Moved the cattle out several weeks ago and forgot about it. Weeds were tall and it was still going strong. Next battery will be a deep cycle marine of some smaller size for easier moving.
I have several small solar parmak's and one big one. The big one was about $275 from Jeffers, but shocks through brush and grass. I've never had problems with any of them - the newer solar powered ones have plenty of power, I wouldn't buy an electric one, they're just not mobile enough.