I had an 86 Cavalier do that when the alternator died. Had just enough charging capacity to get me down the highway, but once I hit the city, things started going bonkers.
Mostly engine management systems started to go haywire, all sorts of indicator lights came on, etc.
I managed to limp it over to my favorite mechanic. By the time I got there, it completely died, and wouldn't restart.
Later that afternoon, new alternator installed, and I was off and running.
It's not the OVP, it's the alternator...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car