This is Nancy Kress' "Against a Crooked Stile" (1979); ISFDb lists a German translation in Isaac Asimovs Science Fiction Magazin 4. Folge (1980).
Jorry Whitfield lives with his drunk, abusive father Clayte, who is afraid of the power lines, but it is not obvious that they actually would harm him.
It doesn't appear that Clayte has a medical condition, but a representative of the power company does warn him about a potential threat to pacemakers:
"Uh...just one more thing, Whitfield. You don't wear a pacemaker, do you? From heart surgery? The company is... uh... advising all residents with the demand-type cardiac pacemakers to remain outside the right of way. Purely as a precautionary measure."
Sometime before the story starts Clayte has broken Jorry's arm while beating him, so Jorry tries to spend as much time away as he can get away with. One day while lazing around under the lines he meets Tom Crowell, who works for an Environmental Study Association that is concerned about the effects of the new 1000kV lines. Tom has 2 sets of mice, one in normal cages and the other in Faraday cages as a control.
Jorry becomes friends with Tom, hangs out with him and does small things to help, like feeding the mice. One day Jerry flees from another confrontation, running to the base of a tower. The tower is struck by lightning and he discovers he can sense fear in the mice as a red halo and a chalky smell. He tests the mouse in the Faraday cage, and it also shows an aura, so Jorry realizes that the change is in him.
The story ends with Jorry seeing his dad in the distance, and his red halo of fear, and heading to a friend's place where Tom is boarding.
The story was first published in Isaac Asimov's Science Fiction Magazine, May 1979, and you can read it at the Internet Archive.