BTW, most newer caps charge themselves.
The stinger i had in my jetta had a voltage display that would actually show the stored charge, rather than system voltage, with a warning alarm that sounded while it was charging, and when it was discharged below 12v. I'm pretty sure that's how most of them work.
I don't know if it actually did anything or not, i was only running 600w rms on my 60a alty, no dimming.