My new Chennic dc-dc unit was showing some voltage sag when the vacuum pump kicked in... noticible only at night when I had headlights going. It caused a momentary headlight 'blink', and was enough to make the radio blink as well! I looked at the capacitors that the stereo guys use, but they are pretty big and expensive. I ended up finding a very small (1.3aH) 12v sealed lead battery for less than $20, and just put this in as an auxilary battery. My dc-dc is 'always on', so it should keep the little battery up, and the battery can pick up the slack when the vacuum pump or any other 12v load causes a momentary voltage sag. Update 5/11/2012: The tiny battery really just wasn't quite cutting it, I still had a blink. I then tried a big 2F capacitor (made for big auto stereos), but that didn't really do it either. I switched to a bigger ATV starter battery , and this DOES work to eliminate all blink. It would probably be best to add an idiot light sensing if and when dc-dc output fails and aux. battery starts draining, but this is a little out of my league to design, I'll have to rely on someone else posting partslist and fabrication tips. ;)