I've been wondering about this too & finally got this guy at work to hook up his radar detector in my car since it has a digital voltage readout for whatever reason. So at lunch yesterday we hooked it up in my car (plugs into cig lighter)to check voltage. I have stock radio, almost 4 yr old stock battery, original alternator, UDP & no other extraneous power hungry devices. At idle without AC,lights, fan,radio or wipers it hung around 12.9 - 13.6. Driving was pretty much solid 14.0, never saw much higher than that regardless of rpm. Started adding things while idling. Radio/CD made pretty much no difference at mid-hi vol - maybe couple of tenths. Lights/fogs a few more, AC few more, same with wipers, etc. With everything on at once (in gear or not) idling was anywhere from 11.6 - 12.8 but mostly right above 12. Once again while driving went right back to 14.0. Pretty much anything over 1500 rpms pegged it at 14. Makes me wonder about a farad capacitor even tho I have no crazy stereo just to keep the voltage a little more stable? Maybe just newer battery? Still no options for a higher output alternator for our cars? (not crazy higher) Keeps the battery charged enough for every day driving so still just in wondering mode. Any thoughts on these things?