I noticed a post about this that was almost a year old and there wasn't any information about it or anything. Has anyone tried this since then? It sounds promising, but due to the little I can find on this I don't want to get my hopes up... Please share any information you may have! Thanks!
Do you mean this? http://www.sigmaautomotive.com/HVS/hvs.php Sounds like the product is a capacitor connected to the terminals of the 12V battery. Having extra capacitor connected to the battery can suppress fluctuations or noise on the 12V line. Not sure how this can increase horse power/MPG and reduce emission like they said on the website. Plus, the 12V is sourced by the inverters, which should be pretty well regulated. Unless you have a huge drain (like after market amps and what not), I don't see how this can help.
If your car is having electrical issues, then this may smooth them out a bit. Like if your car has a flaky alternator or electrical system, I could see this helping to maintain a constant current flow, but it's pretty useless in the Prius and cars in good running order.
