There are three kinds – solar, 110 V (plug-in, supposed to be kept indoors, although I know many people do not), and DC (deep cycle battery powered).
I bought this one:
http://www.valleyvet.com/ct_detail.html?pgguid=63714a46-814d-11d5-a192-00b0d0204ae5
I am putting up Horseguard tape and they recommended using a charger that puts out 2 Joules or higher. Eventually, I will connect my deep cycle battery to a solar panel that will keep it charged (must have one big enough to push out enough volts). Until then, the battery will require charging, probably once a month or so, but I have access to big charger so no problem.
Joules is a measure of energy that, in fencing terms, references the amount of energy that will “shock” when the animal touches the fence. The voltage is a measure of how much current will be pushing through the fence and the resistance that is caused by the length, material, moisture, weeds, whatever on your fence.
Also keep in mind that, like voltage, joules will vary with the load on the charger as well. All you can use to comparison shop is the output joule rating and voltage tables.
So you could have a charger that has very high voltage, but if the joule rating is very low (like 0.5), a lower proportion of that energy shocks the animal.
Solar chargers generally put out very low joules and their voltage is highly variable depending on how efficient the panel is and how much sunlight there is. They are good for small applications, but also need batteries replaced. You can get larger powered ones but they are very expensive.
DC powered ones can produce a lot more power – I went that direction because I will not have power out by my fencing for a while unless you count really long extension cords. It’s not Canada down here so I can’t speak to the battery freezing thing. You could insulate your battery in many ways and run cables out to the charger depending on your layout. Although -26C just makes my brain hurt, I hate winter, aaaahhhh! It is 21 C right now. +21!
I also VERY strongly considered this one:
http://www.kencove.com/fence/dual+purpose+energizers_detail_EXD3.php
You can plug it in OR use a deep cycle battery and it’s got lots of power. I would have gone for it, but the extra $110 I needed for hay. In your case, you could plug it in in the winter if battery freezing is a problem for you and then run it off a battery in the summer to save electricity.