So, my V3 is arriving today, and, the more I read it seems that I should have ordered the 6v version, but anyways, I can just change the jumpers later right?
The 6v and 12v V3s are identical physically, they're simply calibrated differently.
A 6v V3 will run on a >= 6v battery. Only catch: the low battery indicator and auto-shutoff features may not work properly because they're calibrated for a 6v SLA battery - specifically, low battery indicator set to trigger at 5.75v and auto-shutoff at 5v. If you use a battery with a low battery indicator, like the popular li-ion batteries, it's no big deal and not really necessary to recalibrate.
A 12v V3 battery will run on a >= 12v battery. It will not run on a battery < 12v (e.g. 9v li-ion) because the low battery indicator is set to trigger at 11.5v and auto-shutoff at 10v. In this case, you'll need to recalibrate.
To recalibrate, see the
V3 voltage calibration PDF from Grace Design.
For now though, because I want to run this tomorrow night, I have an existing 12v pack that I have used for my MT 24/96 before upgrading to the 744. See here for pics of setup for Microtrack:
http://www.branas.org/files/HowTo/IMG_1063-small.jpg
I was comfortable running this to the Microtrack previously because the cigarette plug/usb combination I know had some kind of fuse in it. But now, if I go straight to the V3, should I put a fuse or something inline? What would you suggest? Any help appreciated.
Yeah, you should use a fuse. But if you're only going to use it once or twice, it's not critical, just a calculated risk. I recommend using a 9v / 5400 mAH li-ion batt with the V3 - light and compact with good run-times. These are marketed as universal DVD batteries and sold under various brands / models: Lenmar DVD-U9, Initial RB-270, Memorex (sorry, forget the model), etc.