When jumping a car with a V8, I messed up the electronics in my 2001 Elantra

No sparks, no arching, no metal melting at terminals The thing is that big old Plymouth Volare V8 never turned over so how could I have blown the computer on the Hyundai? I could see the daylights dim on the Hyundai every time I turned the Volares ignition After work today I got home, and when I turned the car off I heard an electronic feedback type of noise and no dome light when I opened the door Now I just work 10 minutes away in stop and go traffic so I took the car on the highway and drove it 20 minutes before sunset. When I got home and shut the car off I did not hear that feedback noise and the door light, dome light went on when I opened the door. Could battery have broken cells that are not affecting it at times and is affecting it at other times... Either the electronics are up or down, there is no inbetween, usually with a dying battery you will have a weakening dome light, this is different, there is power or it's completely dead!