|Cool. I don't really feel authoritative enough to do a tut on it. I follow battery technology developments with a passion because it's fascinating, and basically driven by the need to develop the electric vehicle market, but I don't consider myself "clued up" on the subject... But I'll do a tut on installing a VSR (voltage sensitive relay). I have ordered some online but they will take time getting here. Basically, it's a relay that, installed in your 2 battery system, automates the charging of the secondary (house) battery. I currently have a manual switch and my memory is getting bad ;-)
Incidentally, there are some battery boosters that work entirely with ultracapacitors. They don't have their own internal battery, instead, using residual low voltage from your "dead" battery to load up a capacitor. This takes anything up to about 3 minutes, but if your battery is at say 10V, it could take as little as 10 seconds. It then provides enough energy from the ultracapacitor to start the car. Biggest benefit from capacitors is their charge and discharge rates... Instant compared to a normal lead acid battery. In time, I believe we will see much smaller batteries used in cars but in conjunction with supercapacitors purely for cranking power.