Electric fence charging of peripheral devices
I did one of these back in 1993 .It charged a 7AH 12V gell battery.I volt limited it at 13.8 V which was the recommended float voltage from PORTALAC .I had something that made a average charging current of from memory 100mA .This was with an off the shelf electric fence with some high voltage resistors and capacitors to crudely emulate a real fence.I used a transformer out of another electric fence backwards to charge some caps .The caps were dropped down into a battery.Yes it can be done if you want a small amount of power from a big fence .But this never went into production due to lack of demand and never got beyond a birds nest on a workbench.