While driving the vehicle on a local road at around 40 mph, check electrical system light came on and I heard a pop sound behind me. The vehicle would suddenly go no faster than 30 mph. Upon further driving, for additional quarter mile, it would drive no faster than 12 mph. I was able to very slowly drive it 1.5 mi back home. Once I arrive home, the vehicle was no longer operational. I confirmed that the 12-volt battery was at an extremely low charge and having the vehicle on would not charge the 12 volt battery. I believe the ICCU failed. I am waiting for Hyundai to further diagnose this.