[BrianG]

A quick and dirty estimate to get amperage required is simply take charger wattage and divide by 10v instead of 12v. Using a lower number accounts for charger efficiency losses and a little extra wiggle room. If you do the full calculation for, say, a 350w charger: (350w/85%)/12v=34A. The quick and dirty method gives you 350w/10v=35A. Pretty darn close for estimation purposes.

On the house fire thing, that makes a difference. I personally would never simply twist and tape wires. Heck, I don't even like wire nuts (which are legal in elec boxes) because the wires are still exposed to air, oxidize which increases contact resistance. The only connection I like is soldering - when done right.