There are no NiCd batteries in a Norman 20/20 pack. This is an A/C strobe pack.
You blew a capacitor (or two). It's pretty alarming, but not unusual, and can happen with any strobe pack, particularly as they get older. A place like the Flash Clinic in New York (www.flashclinic.com) can replace the capacitors.
I once had a capacitor blow in a densitometer. This was even more strange, but the capacitors in densitometers are considerably smaller than the ones in studio strobe packs.