'Fraid you are going to have to retrain them to the electric.
To do this, you'll need to create a small fenced area (maybe around their ark) say 20ft * 10ft, and loosly fence this with stock wire (few posts in the ground, doesn't need to be professional - say 6 vertical posts - one in each corner and an extra one on the long sides, 25 m stock wire - total cost say £40). Put electric on the inside. If you are not already using horse tape (the white stuff) then change to this - pigs see it much more clearly than polywire or just wire.
Pigs will touch the electric, but not be able to go forward through the stockwire, so will back off. Leave them in this for three days, so that they get used to this again. Then remove the stockwire or move them back to old area.
Use two strands of horse tape in their old area - one 6 inches above the ground, and the other slightly higher to give a visible barrier at shoulder height. Again horse tape makes this "barrier" much more obvious
Finally make sure battery doersn't run out again !