For the past three years I've been using car batteries, all cast asides that had reached the point they had trouble starting the car. This was sort of OK until I got a new
fence charger this summer, with an average current draw of 120mA to 300mA. At the same time I also got a 20W
solar panel and everything was pretty good during the summer (
solar panel receiving
enough sunlight to run the
fence during the day
and charge the battery for night. I did notice though that when I got out the animals early in the morning that the fence was blinking red (indication of low battery, output pulse only ever 15 seconds to 60 seconds, instead of once a second). Now its well past the equinox, the sun is low and often behind clouds, the solar panel often doesn't even contribute enough to run the fence during the day, and the car battery was giving up the ghost without any "new" used batteries coming.
I bit the bullet to buy a deep cycle battery (wet- waterable cells). It is the best decision I've made with that electric net fencing and my animals (other than eventually getting permanent electric fencing!). After a week the 105Ah battery was half discharged. I've got it now on the charger and a small 20Ah SLA running the fence till tomorrow morning when I put the big battery back. It could last even longer, but the deeper the battery is discharged the shorter its life. I bought this size of battery after a long comparison of different batteries, costs, weight, lifespan. As long as I charge it at 50% discharge (once a week) then it
should last 9 years.
I recommend anyone who has got a 12V fence charger to make sure to get a deep discharge (traction) battery (unless you have a constant stream of
free old car batteries). Don't make the mistake of buying a car starter battery for an electric fence.