Hi, This is a continuation of my first reply...
Our solar chargers last about two and half weeks without sun once they have been initially charged - We use Gallagher - solar energizers but I'm sure other brands will do the same. We live in Maine & have one that uses a 12 volt rechargeable battery and one that uses a 6 volt and have never had a problem. We use the smaller one as it is more portable for changing fence lines but it charges up to 10 miles of fencing and holds a charge just as well as the larger one.
Be sure to place the solar panel at an angle that gets the most sun for the longest period of the day - also be sure to ground it properly with ground rods - improper grounding is the cause of most electric and solar fencing to not work properly and can drain your battery on a solar energizer.For a small paddocks you can usually mange with one ground rod for large acreage at least 3 of them 10 feet apart, also if you live dry and rocky areas you'll need more ground rods than if you live in moister areas like Maine. Depending the charger you will charge the energizer for about three days before you attach it to the fence,so you'll have to weather watch to be sure you'll get the sun you need for the initial charge.
Sometimes they will suggest overkill on the ground rods, we only have one in our 5 acre pasture and it's been up and running for 6 years without any issues the fence always works. We have not had to replace the battery yet.
Whom ever you get the charger from will have all the info you need to do it right. It might seem complicated as they are explaining the 'how to' but it's really simple. I mention that because the first time I decided to install my own fencing and chargers - as the guy was explaining it to me I was like oh boy LOL! He really made it a lot more complicated that it really is - I figures it out. I do all the solar/electrical fencing myself and have helped friends do theirs as well. So don't be intimidated =;->
In the meantime if you want ta emporary fix that works try the product below - most Home Depot or hardware type stores sell it or you can order it online. It REALLY STINKS but DOES WORK. It is a natural product that is rain resistant. If you do get it - wear a mask when you apply it.
It is natural for horses to chew - they are grazing animals after all and plenty of them love wood . If you grain her try replacing the grain with extra hay in the pasture for more chewing time and even a nice pine log works well in the paddock to help satiate the need to chew.